TCP MSS adjustment

This feature adds support for adjustment of MSS of TCP packets with SYN flag according to access/aggregation network to prevent fragmentation of upstream and downstream TCP packets using ISA-BB.

There are two modes of adjustment operations supported: TCP MSS Adjustment for ESM Hosts, and TCP MSS Adjustment for NAT Services.

For TCP MSS adjust using ISA2-AA, see section AQP for the AQP rules.

This feature adds support for adjustment of the MSS size of TCP packets with SYN flag according to the access/aggregation network to prevent fragmentation of upstream and downstream TCP packets using ISA-BB diverted by IP/IPv6 filter actions.

The following ESM host types are supported:

• IPv4/IPv6 IPoE hosts

• locally terminated PPPoE hosts (without L2TP LAC)

• L2TP LNS hosts

The configuration steps are as follows:

1. Create a NAT group used for an MSS adjustment.

   config>isa
   nat-group 1
   active-mda-limit 2
   mda 1/1
   mda 1/2
   

2. Associate the NAT group with a routing instance and configure the MSS value.

   config>router
   config>service>vprn
   mss-adjust-group 1 segment-size 1452
   

   Note: Unless there are dedicated ISAs or ESAs for MSS adjustment, an existing NAT group or WLAN-GW group can be referenced. If multiple NAT or WLAN-GW groups reference the same ISA or ESA, the NAT or WLAN-GW groups become inactive. MSS adjustment does not function correctly if it references an inactive NAT or WLAN-GW group.

3. Create an IPv4/IPv6 filter to perform an MSS adjust.

   config>filter>ip-filter>entry
   egress-pbr default-load-balancing
   match tcp-syn
   action tcp-mss-adjust
   config>filter>ipv6-filter>entry
   match tcp-syn
   action tcp-mss-adjust
   

4. Apply an IPv4/IPv6 filter to the SLA profile.

This feature provides MSS adjustment for TCP packets to be translated by NAT services.

The configuration steps are as follows:

1. Create a NAT-group used for NAT services with MSS adjustment.

   config>isa
      nat-group 1
         active-mda-limit 2
         mda 1/1
         mda 1/2
   

2. Create a NAT-policy that also adjusts MSS.

   config>service>nat
      nat-policy "policy-for-mss-adjust" crate
         tcp-mss-adjust 1452