Default Address Family For Show Commands; Tcp Maximum Segment Size; Per Neighbor Tcp Mss - Cisco ASR 9000 Series Routing Configuration Manual

Default Address Family for show Commands

reflector uses different communities for best-path and multi-path. This feature allows BGP to signal the local
decision done by RR or Border Router. With this new feature, selected by RR using community-string (if
is-best-path then community 100:100). The controller checks which best path is sent to all R's. Border Gateway
Protocol routers receive multiple paths to the same destination. While carrying out best path computation
there will be one best path, sometimes equal and few non-equal paths. Thus, the requirement for abest-path
and is-equal-best-path.
The BGP best path algorithm decides the best path in the IP routing table and used for forwarding traffic. This
enhancement within the RPL allows creating policy to take decisions. Adding community-string for local
selection of best path. With introduction of BGP Additional Path (Add Path), BGP now signals more than the
best Path. BGP can signal the best path and the entire path equivalent to the best path. This is in accordance
to the BGP multi-path rules and all backup paths.
Default Address Family for show Commands
Most of the show commands provide address family (AFI) and subaddress family (SAFI) arguments (see
RFC 1700 and RFC 2858 for information on AFI and SAFI). The Cisco IOS XR software parser provides the
ability to set the afi and safi so that it is not necessary to specify them while running a show command. The
parser commands are:
• set default-afi { ipv4 | ipv6 | all }
• set default-safi { unicast | multicast | all }
The parser automatically sets the default afi value to ipv4 and default safi value to unicast . It is necessary
to use only the parser commands to change the default afi value from ipv4 or default safi value from unicast
. Any afi or safi keyword specified in a show command overrides the values set using the parser commands.
Use the following show default-afi-safi-vrf command to check the currently set value of the afi and safi.

TCP Maximum Segment Size

Maximum Segment Size (MSS) is the largest amount of data that a computer or a communication device can
receive in a single, unfragmented TCP segment. All TCP sessions are bounded by a limit on the number of
bytes that can be transported in a single packet; this limit is MSS. TCP breaks up packets into chunks in a
transmit queue before passing packets down to the IP layer.
The TCP MSS value is dependent on the maximum transmission unit (MTU) of an interface, which is the
maximum length of data that can be transmitted by a protocol at one instance. The maximum TCP packet
length is determined by both the MTU of the outbound interface on the source device and the MSS announced
by the destination device during the TCP setup process. The closer the MSS is to the MTU, the more efficient
is the transfer of BGP messages. Each direction of data flow can use a different MSS value.

Per Neighbor TCP MSS

The per neighbor TCP MSS feature allows you to create unique TCP MSS profiles for each neighbor. Per
neighbor TCP MSS is supported in two modes: neighbor group and session group. Before, TCP MSS
configuration was available only at the global level in the BGP configuration.
The per neighbor TCP MSS feature allows you to:
• Enable per neighbor TCP MSS configuration.
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
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Implementing BGP