IPv4 DHCP Hosts

The DHCP protocol is used by a DHCP server to dynamically assign IP addresses and other optional configuration parameters on request of DHCP clients. These parameters are leased by the DHCP server for a duration specified by the lease time.

The DHCP lease process is outlined in DHCP Lease Process.

When a DHCP client boots, a DHCP discover message is broadcast on the local subnet (dest-ip = 255.255.255.255).

A DHCP server in the local subnet responds with a unicast DHCP offer message containing the your ip address field as well as other configuration parameters in the option fields (such as subnet mask, default gateway, DNS server IP addresses, lease time, etc.).

The DHCP client responds with a DHCP request message to accept the parameters specified in the DHCP offer. The DHCP request is also broadcast on the local subnet.

The DHCP server acknowledges the DHCP request with a unicast DHCP ack message.

When the DHCP client receives a DHCP ack from the server, it is said to be in the bound state.

When half of the lease time has expired, the DHCP client tries to renew the lease. It will send a unicast DHCP request message to the DHCP server. The DHCP server will reply to the request with a unicast DHCP ack to the client.

If the renew failed, a rebind is attempted by default at 7/8 of the lease time. It will send a broadcast DHCP request message.

Before disconnecting from the local subnet, a DHCP client may return its lease by sending a DHCP release message to the DHCP server.

In case no DHCP server is present in the subnet of the DHCP client, a DHCP relay agent is needed to forward the broadcast DHCP discover/request messages on behalf of the DHCP client to a DHCP server located on a different subnet. The DHCP relay agent will add the gateway IP address field to the messages and send them as unicast to the DHCP server IP address. The DHCP server in this case will respond to the DHCP relay agent using a unicast frame. The DHCP relay agent forwards the DHCP server messages in broadcast frames on the DHCP client subnet.

DHCP client originated messages (discover, request, release) must be snooped (intercepted and sent to the control plane for further processing) to enable DHCP Option 82 insertion, authentication through local user database (LUDB), AAA/RADIUS or AAA/Diameter, and releasing the DHCP host session state.

For Bridged CO, DHCP snooping must be enabled explicitly on the subscriber SAP:

# Bridged CO @ BSA-1
configure
    service
        vpls 1
            ---snip---
            sap 1/1/3:1 split-horizon-group "rshg-1" create
                description "sub-1"
                dhcp
                    snoop
                    no shutdown
                exit
            exit
         exit
     exit
exit

DHCP server originated messages (offer, ack, nak, etc.) must be snooped to enable DHCP Option 82 removal, lease state population and/or ESM functions.

For Bridged CO, DHCP snooping must be enabled explicitly on all SDPs and/or SAPs that should provide connectivity to the DHCP server:

# Bridged CO @ BSA-1
configure
    service
        vpls 1
            ---snip---
            spoke-sdp 1:1 create
                dhcp
                    snoop
                exit
                no shutdown
            exit
         exit
     exit
exit

For Routed CO, DHCP snooping is implicitly enabled by configuring a DHCP relay agent (DHCP Relay Agent): All DHCP messages received on a routed network interface will be snooped, that is, they are intercepted and sent to the control plane for further processing.

For Bridged CO, the DHCP relay agent function is configured in the IP edge (BSR), at the regular interface level:

# Bridged CO @ BSR-1
configure 
    service
        vprn 1
            ---snip---
            interface "int-BSA1-p2mp-1" create
                description "Bridged CO"
                address 10.1.0.254/16
                dhcp
                    server 172.16.0.1
                    trusted
                    gi-address 10.1.0.254
                    no shutdown
                exit
                ---snip---
                ip-mtu 1500
                spoke-sdp 1:1 create
                    no shutdown
                exit
            exit
         exit
     exit
exit

For Routed CO, the DHCP relay agent function must be configured at BSR-1 group-interface level where the DHCP host will be instantiated:

# Routed CO @ BSR-1
configure 
    service
        vprn 1
            ---snip---
            subscriber-interface "sub-int-1" create
                description "Routed CO"
                address 10.2.0.254/16
                group-interface "group-int-1" create
                    ---snip---
                    dhcp
                        server 172.16.0.1
                        trusted
                        ---snip---
                        gi-address 10.2.0.254
                        no shutdown
                    exit
                exit
            exit
        exit
    exit
exit

The server command defines the IP address of the DHCP server and must be reachable in the same routing instance as where the (subscriber-)interface is defined.

The trusted command makes the interface a trusted interface and enables Option 82 insertion by a Layer 2 DHCP relay agent (see DHCP Options (Relay Agent Information)).

The gi-address must be a locally configured IP address on the (subscriber-) interface. By default the DHCP messages relayed to the DHCP server use the outgoing interface IP address as source IP address. By specifying the optional src-ip-addr flag, the configured gi-address is used as the source IP address:

CLI Syntax:

— gi-address 10.2.0.254 src-ip-addr

A Layer 2 DHCP relay agent (such as BSAN or BSA) can add DHCP Option 82 information and leave the gi-address field to 0.0.0.0. The gi-address is the gateway IP address, filled in by the DHCP relay agent. An incoming DHCP discover with Option 82 present and gi-address field = 0.0.0.0 will be dropped by the DHCP relay agent according the RFC. The Rx Untrusted Packets and client Packets Discarded counters are increased in the DHCP statistics.

Output from DHCP debug log on BSR-1:

158 2019/04/09 14:44:32.78 CET MINOR: DEBUG #2001 vprn1 PIP
"PIP: DHCP
instance 2 (1), interface index 4 (group-int-1), 
   DROPPED DHCP Boot Request on Interface group-int-1 (1/1/3:1) Port 67
   Problem: message is received from an untrusted client

Therefore, the DHCP relay agent should be configured as trusted to allow DHCP Option 82 insertion by a Layer 2 DHCP relay agent.

In Bridged CO, when DHCP snooping is enabled on a VPLS SAP, DHCP Option 82 relay agent information can be altered or added on an incoming DHCP discover/request. This is referred to as a Layer 2 DHCP relay agent function.

In Routed CO, a DHCP relay agent can alter or add the DHCP Option 82 relay agent information on an incoming DHCP discover/request.

Supported DHCP Option 82 sub-options and their format are listed in Supported DHCP Option 82 Sub-Options:

Table 1. Supported DHCP Option 82 Sub-Options

Option 82 Sub-Option	Format	Example
Opt82 [1] Circuit ID (Routed CO)	ifindex — 32 bit virtual router ID followed by a 32 bit ifindex in hex	00 00 00 02 00 00 00 04
	sap-id [sap id in ascii]	1/1/3:1
	ascii-tuple [system-name|service-id|group-interface|sap-id]
	vlan-ascii-tuple [system-name|service-id|group-interface|dot1p|vlan-id]	‟BSR-1|1|group-int-1|0|1”
Opt82 [1] Circuit ID (Bridged CO)	ascii-tuple [system-name|service-id|sap-id]	‟BSA-1|1|1/1/2:1”
	vlan-ascii-tuple [system-name|service-id|sap-id |dot1p|vlan-id]	‟BSA-1|1|1/1/2:1|0|1”
Opt82 [2] Remote ID (Bridged and Routed CO)	MAC [client hw address in hex]	fe fd 00 02 45 00
	string (max. 32 chars)	‟Opt-82 [2] – Remote ID”
Opt82 [9] Vendor Specific (Bridged and Routed CO)	[1] system-id [hostname in ascii]	‟BSA-1” or ‟BSR-1”
	[2] client-mac-address [client hw address in hex]	fe fd 00 02 45 00
	[3] service-id	1
	[4] sap-id [sap id in ascii]	‟1/1/2:1”
	[5] string (max. 32 chars)	‟Opt-82 [9] [5] – string”
Opt82 [9] Vendor Specific (Routed CO)	[13] pool-name [dhcp pool name from Radius/Local User DB in ascii	‟dhcp-pool-1”

Following actions can be taken on incoming DHCP discover/request:

• replace

• drop

• keep (default)

Replace

At ingress:

If present, remove all the Option 82 information from the incoming DHCP discover/request. Insert the configured DHCP options before forwarding to the DHCP relay agent or DHCP server.

At egress:

Remove all Option 82 information from the incoming DHCP offer/ack before forwarding to the client.

# Bridged CO @ BSA-1
configure 
    service
        vpls 1
            ---snip---
            sap 1/1/3:1 split-horizon-group "rshg-1" create
                description "sub-1"
                dhcp
                    snoop
                    option
                        action replace
                        remote-id string "Opt-82 [2] - Remote ID"
                        vendor-specific-option
                            system-id
                            client-mac-address
                            service-id
                            sap-id
                            string "Opt-82 [9][5] - Vendor ID"
                        exit
                    exit
                    no shutdown
                exit
            exit
         exit
     exit
exit

# Routed CO @ BSR-1
configure 
    service
        vprn 1
            ---snip---
            subscriber-interface "sub-int-1" create
                description "Routed CO"
                address 10.2.0.254/16
                group-interface "group-int-1" create
                    ---snip---
                    dhcp
                        option
                            action replace
                            circuit-id
                            remote-id string "Opt-82 [2] Remote-ID"
                            vendor-specific-option
                                system-id
                                client-mac-address
                                pool-name
                                service-id
                                sap-id
                                string "Opt-82 [9][5] string"
                            exit
                        exit
                        server 172.16.0.1
                        trusted
                        ---snip---
                        gi-address 10.2.0.254
                        no shutdown
                    exit
                exit
            exit
         exit
     exit
exit

Drop

Drop all incoming DHCP discover/request with Option 82 information present.

Incoming DHCP discover/request without Option 82 information will be forwarded to (Bridged CO) or processed by (Routed CO) the DHCP relay agent as is, ignoring the configured options.

# Bridged CO @ BSA-1
configure 
    service
        vpls 1
        ---snip---
                sap 1/1/3:1 split-horizon-group "rshg-1" create
                description "sub-1"
                dhcp
                    snoop
                    option
                        action drop
                    exit
                exit
            exit
        exit
    exit
exit

# Routed CO @ BSR-1
configure
    service
        vprn 1
            ---snip---
            subscriber-interface "sub-int-1" create
                description "Routed CO"
                address 10.2.0.254/16
                group-interface "group-int-1" create
                    ---snip---
                    dhcp
                        option
                            action drop
                        exit
                        server 172.16.0.1
                        trusted
                        gi-address 10.2.0.254
                        no shutdown
                    exit
                exit
            exit
        exit
    exit
exit

The output from the DHCP debug log on BSA-1 and BSR-1 is as follows:

# Bridged CO @ BSA-1

343 2019/04/10 10:39:28.811 CEST MINOR: DEBUG #2001 Base SVCMGR
"SVCMGR: Dropped DHCP Packet
   VPLS 1, SAP 1/1/3:1
 
   Problem: port config doesn't allow BOOTP/DHCP packets with option 82

# Routed CO @ BSR-1

730 2019/04/10 10:42:58.978 CEST MINOR: DEBUG #2001 vprn1 PIP
"PIP: DHCP
instance 2 (1), interface index 6 (group-int-1),
   DROPPED DHCP Boot Request on Interface group-int-1 (1/1/3:1) Port 67
   Problem: action drop is configured and packet contains option 82

The Clients Packets Dropped counter is increased in the DHCP statistics:

*A:BSA-1# show service id 1 dhcp statistics
 
=====================================================
DHCP Statistics, service 1
=====================================================
Client Packets Snooped               : 85
Client Packets Forwarded             : 52
Client Packets Dropped               : 9
Client Packets Proxied (RADIUS)      : 0
Client Packets Proxied (Diameter)    : 0
Client Packets Proxied (User-Db)     : 0
Client Packets Proxied (Lease-Split) : 24
Server Packets Snooped               : 43
Server Packets Forwarded             : 19
Server Packets Dropped               : 24
DHCP RELEASEs Spoofed                : 24
DHCP FORCERENEWs Spoofed             : 0
=====================================================
*A:BSA-1#

*A:BSR-1# show service id 1 dhcp statistics
 
====================================================================
DHCP Global Statistics, service 1
====================================================================
Rx Packets                           : 287
Tx Packets                           : 251
Rx Malformed Packets                 : 0
Rx Untrusted Packets                 : 0
Client Packets Discarded             : 36
Client Packets Relayed               : 124
Client Packets Snooped               : 6
Client Packets Proxied (RADIUS)      : 0
Client Packets Proxied (Diameter)    : 0
Client Packets Proxied (User-Db)     : 0
Client Packets Proxied (Lease-Split) : 0
Server Packets Discarded             : 52
Server Packets Relayed               : 69
Server Packets Snooped               : 0
DHCP RELEASEs Spoofed                : 52
DHCP FORCERENEWs Spoofed             : 0
Client packets streamed              : 0
====================================================================
*A:BSR-1#

Keep (Default)

At ingress: Incoming DHCP discover/request without Option 82 information will be forwarded to (Bridged CO) or processed by (Routed CO) the DHCP relay agent as is, ignoring any configured option.

At ingress for incoming DHCP discover/request with Option 82 information present. Configured vendor specific options will be merged with the existing Option 82 information before sending to (Routed CO) or processing by (Routed CO) the DHCP relay agent. Configured Circuit ID and Remote ID options will be ignored.

At egress: Remove Option 82 vendor specific information from the incoming DHCP offer/ack before forwarding to the client. Other existing DHCP Option 82 information is retained.

# Bridged CO @ BSA-1
configure 
    service
        vpls 1
            ---snip---
            sap 1/1/3:1 split-horizon-group "rshg-1" create
                description "sub-1"
                dhcp
                    snoop
                    option
                        action keep
                    exit
                exit
            exit
        exit
    exit

# Routed CO @ BSR-1
configure 
    service
        vprn 1
            ---snip---
            subscriber-interface "sub-int-1" create
                description "Routed CO"
                address 10.2.0.254/16
                group-interface "group-int-1" create
                    ---snip---
                    dhcp
                        option
                            action keep
                        exit
                        server 172.16.0.1
                        trusted
                        gi-address 10.2.0.254
                        no shutdown
                    exit
                exit
            exit
        exit
    exit

The DHCP lease state table keeps track of the DHCP host states. The DHCP lease state table enables subscriber management functions (per-subscriber QoS and accounting) and security functions (dynamic anti-spoof filtering) on the DHCP host.

The DHCP lease information for a specific host is extracted from the DHCP ack message.

Information in DHCP Lease State displays some information stored in the DHCP lease state. The table does not display all information: additional data is added for managed SAPs, DHCPv6, etc.

Table 2. Information in DHCP Lease State

Parameter	Comment
Service ID	Service where the DHCP host is connected
IP Address	IP address of the DHCP host
Client HW Address	Ethernet MAC address of the DHCP host
Subscriber-interface (Routed CO only)	Subscriber interface name where the DHCP host is instantiated
Group-interface (Routed CO only)	Group interface name where the DHCP host is instantiated
SAP	SAP where the DHCP hosts is connected
Up Time	The DHCPv4 host uptime
Remaining Lease Time	The time remaining before the lease expires
Remaining SessionTime	The time remaining before the DHCPv4 host is deleted from the system (updated each time a DHCP renew/rebind occurs)
Persistence Key	Lookup key for this host in the persistency file (see further)
Sub-Ident	ESM: Subscriber ID of the DHCP host
Sub-Profile-String	ESM: Subscriber profile string of the DHCP host
SLA-Profile-String	ESM: SLA profile string of the DHCP host
App-Profile-String	ESM: Application profile string of the DHCP host
Lease ANCP-String	ESM: ANCP string for this DHCP host
Lease Int Dest Id	ESM: Internal destination ID for this DHCP host
Category-Map-Name	ESM: Volume and Time based accounting
Lease Info origin	ESM: Origin for the IP configuration for this host (None, DHCP, RADIUS, etc.)
Ip-Netmask	The IP netmask for this DHCP host
Broadcast-Ip-Addr	The broadcast IP address for this host
Default-Router	The default gateway for this host
Primary-Dns	The primary DNS server for this host
Secondary-Dns	The secondary DNS server for this host
Primary-Nbns	The primary NetBIOS name server for this host
Secondary-Nbns	The secondary NetBIOS name server for this host
ServerLeaseStart	Time and date that the lease for this host started (first DHCP ack received)
ServerLastRenew	Time and date that the lease for this host was last renewed
ServerLeaseEnd	Time and date that the lease for this host will expire
Session-Timeout	The DHCPv4 is deleted when its uptime reaches this value
IPoE|PPP session	Indication if this lease belongs to an IPoE or PPP session, or to no session
Lease-Time	The lease time specified by the DHCPv4 server
DHCP Server Addr	IP address of the DHCP server that allocated the lease for this host
Circuit Id	DHCP Relay Agent information Option 82 Circuit ID content
Remote Id	DHCP Relay Agent information Option 82 Remote ID content
RADIUS User-Name	ESM: Username used in the RADIUS authentication access request

For Bridged CO, the DHCP lease state table can only be populated through explicit configuration with the lease-populate command. The number of leases allowed on the VPLS SAP must be specified. When omitted, a single DHCP host is allowed per SAP.

# Bridged CO @ BSA-1
configure 
    service
        vpls 1
            ---snip---
            sap 1/1/3:1 split-horizon-group "rshg-1" create
                description "sub-1"
                dhcp
                    snoop
                    lease-populate 10
                    no shutdown
                exit
            exit
         exit
     exit
exit

For Routed CO, DHCP lease state table population is enabled by default on a group interface with DHCP configured as no shutdown. The number of leases allowed on each SAP of the group-interface must be configured (by default a single DHCP host is allowed on each SAP):

# Routed CO @ BSR-1
configure 
    service
        vprn 1
            ---snip---
            subscriber-interface "sub-int-1" create
                description "Routed CO"
                address 10.2.0.254/16
                group-interface "group-int-1" create
                    dhcp
                        server 172.16.0.1
                        trusted
                        lease-populate 10
                        gi-address 10.2.0.254
                        no shutdown
                    exit
                exit
            exit
         exit
     exit
exit

To check the DHCP lease state for a particular service, use the show service id <service-id> dhcp lease-state command. Detailed output as well as additional output filtering is available:

*A:BSA-1# show service id 1 dhcp lease-state ?
  - lease-state [wholesaler <service-id>] [sap <sap-id>|sdp <sdp-id:vc-id>|interface <interface-name>|ip-address <ip-address[/mask]>|chaddr <ieee-address>|mac <ieee-address>|{[port <port-id>] [no-inter-dest-id | inter-dest-id <inter-dest-id>]}] [session {none|ipoe}] [detail]

A:BSR-1# show service id 1 dhcp lease-state ?
  - lease-state [wholesaler <service-id>] [sap <sap-id>|sdp <sdp-id:vc-id>|interface <interface-name>|ip-address <ip-address[/mask]>|chaddr <ieee-address>|mac <ieee-address>|{[port <port-id>] [no-inter-dest-id | inter-dest-id <inter-dest-id>]}] [session {none|ipoe}] [detail]

*A:BSA-1# show service id 1 dhcp lease-state mac 00:00:00:11:11:11 detail
 
===============================================================================
DHCP lease states for service 1
===============================================================================
Service ID           : 1
IP Address           : 10.1.0.100
Client HW Address    : 00:00:00:11:11:11
SAP                  : 1/1/3:1
Termination Type     : local
Up Time              : 0d 01:46:22
Remaining Lease Time : 0d 10:13:37
Remaining SessionTime: N/A
Persistence Key      : N/A
 
Sub-Ident            : "sub-11"
Sub-Profile-String   : "sub-profile-1"
SLA-Profile-String   : "sla-profile-1"
App-Profile-String   : ""
Lease ANCP-String    : ""
Lease Int Dest Id    : ""
Category-Map-Name    : ""
 
Lease Info origin    : DHCP
 
Ip-Netmask           : 255.255.0.0
Broadcast-Ip-Addr    : 10.1.255.255
Default-Router       : 10.1.0.254
Primary-Dns          : N/A
Secondary-Dns        : N/A
Primary-Nbns         : N/A
Secondary-Nbns       : N/A
 
ServerLeaseStart     : 04/09/2019 13:47:36
ServerLastRenew      : 04/09/2019 13:47:36
ServerLeaseEnd       : 04/10/2019 01:47:36
Session-Timeout      : N/A
IPoE|PPP session     : No
Lease-Time           : 0d 12:00:00
DHCP Server Addr     : 172.16.0.1
Radius User-Name     : "00:00:00:11:11:11"
-------------------------------------------------------------------------------
Number of lease states : 1
===============================================================================
*A:BSA-1#

*A:BSR-1# show service id 1 dhcp lease-state mac 00:00:00:33:33:33 detail
 
===============================================================================
DHCP lease states for service 1
===============================================================================
Service ID           : 1
IP Address           : 10.2.0.102
Client HW Address    : 00:00:00:33:33:33
Subscriber-interface : sub-int-1
Group-interface      : group-int-1
SAP                  : 1/1/3:1
Termination Type     : local
Up Time              : 0d 01:43:48
Remaining Lease Time : 0d 10:16:12
Remaining SessionTime: N/A
Persistence Key      : N/A
 
Sub-Ident            : "sub-33"
Sub-Profile-String   : "sub-profile-1"
SLA-Profile-String   : "sla-profile-1"
App-Profile-String   : ""
Lease ANCP-String    : ""
Lease Int Dest Id    : ""
Category-Map-Name    : ""
 
Lease Info origin    : DHCP
 
Ip-Netmask           : 255.255.0.0
Broadcast-Ip-Addr    : 10.2.255.255
Default-Router       : 10.2.0.254
Primary-Dns          : N/A
Secondary-Dns        : N/A
Primary-Nbns         : N/A
Secondary-Nbns       : N/A
 
ServerLeaseStart     : 04/09/2019 13:53:58
ServerLastRenew      : 04/09/2019 13:53:58
ServerLeaseEnd       : 04/10/2019 01:53:58
Session-Timeout      : N/A
IPoE|PPP session     : No
Lease-Time           : 0d 12:00:00
DHCP Server Addr     : 172.16.0.1
Radius User-Name     : "00:00:00:33:33:33"
-------------------------------------------------------------------------------
Number of lease states : 1
===============================================================================
*A:BSR-1#

Snooping the DHCP communication between a DHCP client and a DHCP relay agent/server facilitates the DHCP host instantiation: Upon the reception of a DHCP ack message from the server, the DHCP lease state table is populated. With ESM enabled, a DHCP host is also instantiated. The DHCP host will appear in the subscriber-host table for the service with origin set to DHCP.

*A:BSA-1# show service id 1 subscriber-hosts
 
=============================================================
Subscriber Host table
=============================================================
Sap                    Subscriber               
  IP Address                                    
    MAC Address          PPPoE-SID Origin       
-------------------------------------------------------------
1/1/3:1                sub-11
  10.1.0.100
    00:00:00:11:11:11    N/A       DHCP          
-------------------------------------------------------------
Number of subscriber hosts : 1
=============================================================
*A:BSA-1#

*A:BSR-1# show service id 1 subscriber-hosts 
=============================================================
Subscriber Host table
=============================================================
Sap                    Subscriber                
  IP Address                                     
    MAC Address          PPPoE-SID Origin       Fwding State
-------------------------------------------------------------
1/1/3:1                sub-33
  10.2.0.102
    00:00:00:33:33:33    N/A       DHCP         Fwding
-------------------------------------------------------------
Number of subscriber hosts : 1
=============================================================
*A:BSR-1#

If ESM is enabled, the subscriber-host will also appear in the active subscriber table:

*A:BSR-1# show service active-subscribers
 
===============================================================================
Active Subscribers
===============================================================================
-------------------------------------------------------------------------------
Subscriber sub-33 (sub-profile-1)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
(1) SLA Profile Instance sap:1/1/3:1 - sla:sla-profile-1
-------------------------------------------------------------------------------
IP Address
                MAC Address          Session        Origin       Svc        Fwd
-------------------------------------------------------------------------------
10.2.0.102
                00:00:00:33:33:33    N/A            DHCP         1          Y
-------------------------------------------------------------------------------
 
-------------------------------------------------------------------------------
Number of active subscribers : 1
===============================================================================
*A:BSR-1#

Troubleshooting the DHCP session set-up is done with DHCP debugging:

*A:BSA-1# debug service id 1 dhcp ?
  - dhcp
  - no dhcp

 [no] detail-level    - Configure the DHCP tracing detail level
 [no] mac             - Show DHCP packets for a particular MAC address
 [no] mode            - Configure the DHCP tracing mode
 [no] sap             - Show DHCP packets for a particular SAP
 [no] sdp             - Show DHCP packets for a particular SDP
 
*A:BSA-1#

*A:BSR-1# debug router 1 ip dhcp ?
  - dhcp [interface <ip-int-name>]
  - dhcp mac <ieee-address>
  - dhcp sap <sap-id>
  - no dhcp [interface <ip-int-name>]
  - no dhcp mac <ieee-address>
  - no dhcp sap <sap-id>
 
  ---snip---
 
*A:BSR-1#

For example:

*A:BSA-1# show debug
debug
    service
        id 1
            dhcp
                mode egr-ingr-and-dropped
                detail-level medium
            exit
        exit
    exit
exit
*A:BSA-1#

*A:BSR-1# show debug
debug
    router "1"
        ip
            dhcp
                detail-level medium
                mode egr-ingr-and-dropped
            exit
        exit
    exit
exit
*A:BSR-1#

The example above will log all DHCP packets on the service. When thousands of DHCP hosts are active, fine grained filtering is required: for example look only to dropped packets or look only to packets from a particular MAC address.

To display the debugging information, a dedicated log should be created:

configure
    log
        log-id 1
            description "Send debug log to a buffer in memory"
            from debug-trace
            to memory
            no shutdown
        exit
    exit
exit

The following shows a sample DHCP debug log output (detail-level medium) on BSA-1:

77 2019/04/09 13:58:20.022 CEST MINOR: DEBUG #2001 Base SVCMGR
"SVCMGR: RX DHCP Packet
   VPLS 1, spoke-sdp 1:1
 
   BootReply to UDP port 68
   ciaddr: 0.0.0.0           yiaddr: 10.1.0.102
   siaddr: 172.16.0.1        giaddr: 10.1.0.254
   chaddr: 00:00:00:22:22:22    xid: 0x7
 
   DHCP options:
   [53] Message type: Ack
   [54] DHCP server addr: 172.16.0.1
   [51] Lease time: 43200
   [1] Subnet mask: 255.255.0.0
   [3] Router: 10.1.0.254
   [58] Renew timeout: 21600
   [59] Rebind timeout: 37800
   [28] Broadcast addr: 10.1.255.255
   [255] End
"

During the lifespan of a DHCP host, the DHCP lease state is updated in the system: for example, the remaining lifetime changes after a DHCP renew. To check the lease details from the DHCP host during its lifespan, consult the DHCP lease state details:

*A:BSA-1# show service id 1 dhcp lease-state detail
 
===============================================================================
DHCP lease states for service 1
===============================================================================
Service ID           : 1
IP Address           : 10.1.0.100
Client HW Address    : 00:00:00:11:11:11
SAP                  : 1/1/3:1
Termination Type     : local
Up Time              : 0d 02:09:01
Remaining Lease Time : 0d 09:50:58
Remaining SessionTime: N/A
Persistence Key      : N/A
  
---snip---
  
ServerLeaseStart     : 04/09/2019 13:47:36
ServerLastRenew      : 04/09/2019 13:47:36
ServerLeaseEnd       : 04/10/2019 01:47:36
Session-Timeout      : N/A
IPoE|PPP session     : No
Lease-Time           : 0d 12:00:00
DHCP Server Addr     : 172.16.0.1
Radius User-Name     : "00:00:00:11:11:11"
-------------------------------------------------------------------------------
Number of lease states : 1
===============================================================================
*A:BSA-1#

If the remaining lifetime timer expires before the DHCP session is renewed or rebound, the DHCP lease state is cleared. If ESM is enabled, the DHCP host is removed from the system.

A DHCP host can be manually deleted from the system using following clear command:

*A:BSA-1# clear service id 1 dhcp lease-state ?
  - lease-state all [no-dhcp-release]
  - lease-state [port <port-id>] inter-dest-id <intermediate-destination-id> 
                                                              [no-dhcp-release]
  - lease-state [port <port-id>] no-inter-dest-id [no-dhcp-release]
  - lease-state ip-address <ip-address[/mask]> [no-dhcp-release]
  - lease-state mac <ieee-address> [no-dhcp-release]
  - lease-state port <port-id> [no-dhcp-release]
  - lease-state sap <sap-id> [no-dhcp-release]
  - lease-state sdp <sdp-id:vc-id> [no-dhcp-release]
 
---snip---
                        
*A:BSA-1# clear service id 1 dhcp lease-state ip-address 10.1.0.100

The DHCP lease state is deleted with all related state (such as, anti-spoof filter, ARP table entry). If ESM is enabled, the DHCP host is removed from the system. Optionally, a DHCP release is sent to the DHCP server to notify that the IP address can be released. This is reflected in the DHCP statistics in the DHCP RELEASEs Spoofed counter. Use the no-dhcp-release flag in the clear command if no DHCP release is to be sent when issuing the clear command.

To display a summary overview of the DHCP configuration on a particular service:

*A:BSA-1# show service id 1 dhcp summary
 
========================================================================
DHCP Summary, service 1
========================================================================
Sap/Sdp                Snoop  Used/       Arp Reply   Info     Admin
                              Provided    Agent       Option   State
------------------------------------------------------------------------
sap:1/1/3:1            Yes    0/10        Yes         Keep     Up
sap:1/1/3:2            Yes    0/10        Yes         Keep     Up
sdp:1:1                Yes    N/A         N/A         N/A      N/A
------------------------------------------------------------------------
Number of Entries : 3
------------------------------------------------------------------------
========================================================================
*A:BSA-1#

*A:BSR-1# show service id 1 dhcp summary
 
===============================================================================
DHCP Summary, service 1
===============================================================================
Interface Name                   Arp      Leases Per Interface/ Info    Admin
  SapId/Sdp                      Populate Per Sap Limit         Option  State
-------------------------------------------------------------------------------
group-int-1                      Yes      1/10                  Keep    Up
int-BSA1-p2mp-1                  No       0/0                   Keep    Up
-------------------------------------------------------------------------------
Interfaces: 2
===============================================================================
*A:BSR-1#

The Leases Per Interface/Per Sap Limit field indicates the number of active versus the number of allowed DHCP leases on the SAP, SDP or interface.

To check the DHCP statistics, use the following command:

*A:BSA-1# show service id 1 dhcp statistics
 
=====================================================
DHCP Statistics, service 1
=====================================================
Client Packets Snooped               : 33
Client Packets Forwarded             : 33
Client Packets Dropped               : 0
Client Packets Proxied (RADIUS)      : 0
Client Packets Proxied (Diameter)    : 0
Client Packets Proxied (User-Db)     : 0
Client Packets Proxied (Lease-Split) : 0
Server Packets Snooped               : 12
Server Packets Forwarded             : 12
Server Packets Dropped               : 0
DHCP RELEASEs Spoofed                : 1
DHCP FORCERENEWs Spoofed             : 0
=====================================================
*A:BSA-1#

*A:BSR-1# show service id 1 dhcp statistics
 
====================================================================
DHCP Global Statistics, service 1
====================================================================
Rx Packets                           : 59
Tx Packets                           : 38
Rx Malformed Packets                 : 0
Rx Untrusted Packets                 : 0
Client Packets Discarded             : 21
Client Packets Relayed               : 18
Client Packets Snooped               : 2
Client Packets Proxied (RADIUS)      : 0
Client Packets Proxied (Diameter)    : 0
Client Packets Proxied (User-Db)     : 0
Client Packets Proxied (Lease-Split) : 0
Server Packets Discarded             : 0
Server Packets Relayed               : 18
Server Packets Snooped               : 0
DHCP RELEASEs Spoofed                : 0
DHCP FORCERENEWs Spoofed             : 0
Client packets streamed              : 0
====================================================================
*A:BSR-1#

To clear the DHCP statistics:

*A:BSA-1# clear service id 1 dhcp statistics ?
  - statistics [sap <sap-id> | sdp <sdp-id:vc-id> | 
                               interface <ip-int-name|ip-address>]

 ---snip---
*A:BSA-1#

*A:BSR-1# clear router 1 dhcp statistics ?
  - statistics [<ip-int-name|ip-address>]
 <ip-int-name|ip-ad*> : ip-int-name    - 32 chars max
                        ip-address     - a.b.c.d

 ---snip---
 
*A:BSR-1#

A field technician verifying DSLAM operation often connects and disconnects from different ports rapidly. This will require the node to clear its own DHCP host state, the DHCP server state as well as flush MAC addresses learned within the VPLS network or clear ARP entries from the routing instance.

A DHCP request enters on SAP2. On SAP1 there exists a lease state with the same Client Hardware address. The packet is dropped and a forced SHCV check verifies the existing lease state on SAP1. Three consecutive checks are launched with a timeout of 10 seconds. If the host indeed moved form SAP1 to SAP2, the connectivity check will fail on SAP1. The existing lease state is deleted and a DHCP release message is sent to the DHCP server. Any subsequent DHCP session setup will proceed as normal.

Note that for host mobility to function, host-connectivity-verification must be enabled. Next to periodic connectivity checks, it also enables forced checks triggered by moving hosts.

For Bridged CO, host-connectivity-verify must be enabled on the SAPs. When no interval is specified, it will default to 10 minutes for the periodic connectivity checks.

# Brigded CO
configure
    service
        vpls 1
            sap 1/1/3:1
                host-connectivity-verify source-ip 10.1.0.253
            exit
            sap 1/1/3:2
                host-connectivity-verify source-ip 10.1.0.253
            exit
        exit
    exit
exit

The configured source-ip should be an unused unique ip address in the DHCP client subnet or alternatively use source-ip 0.0.0.0. As the host-connectivity-verify application is sending a unicast ARP to the DHCP host, its ARP table is updated with the configured source-ip and source-mac (chassis MAC if not configured). If you would use an existing IP address, the DHCP host ARP table gets poisoned, breaking the connectivity to that host.

For Routed CO, host-connectivity-verify must be enabled on the group-interface. When no interval is specified, it will default to 10 minutes for the periodic connectivity checks.

# Routed CO
configure
    service
        vprn 1 customer 1 create
            subscriber-interface "sub-int-1" create
                group-interface "group-int-1" create
                    host-connectivity-verify
                exit
            exit
        exit
    exit
exit

The source IP address is not configurable. The source-ip used in the unicast ARP is fixed to the local subscriber interface address in the subnet of the DHCP hosts that is checked for connectivity.