# BGP Session and Address Family Parameters

DevFeed: [BGP Session and Address Family Parameters](<https://devfeed.tech/articles/bgp-session-and-address-family-parameters-11051.md>)

Original publisher: [Read original article](<https://blog.ipspace.net/2024/08/bgp-session-af-parameters/>)

Published: 2024-08-19T04:45:00Z

Content type: tutorial

Language: en

Sources: [ipSpace.net blog](<https://devfeed.tech/sources/ipspace-net-blog.md>)

Topics: [BGP](<https://devfeed.tech/topics/bgp.md>), [configuration](<https://devfeed.tech/topics/configuration.md>), [evpn](<https://devfeed.tech/topics/evpn.md>)

Tags: [bgp](<https://devfeed.tech/tags/bgp.md>), [configuration](<https://devfeed.tech/tags/configuration.md>), [evpn](<https://devfeed.tech/tags/evpn.md>), [ipv4](<https://devfeed.tech/tags/ipv4.md>), [ipv6](<https://devfeed.tech/tags/ipv6.md>), [tcp](<https://devfeed.tech/tags/tcp.md>)

## AI overview

This article explains which BGP parameters belong to the TCP neighbor session and which belong to individual address families. It highlights inconsistent vendor implementations of AS-path controls, including allowas-in, and notes that EVPN may require address-family-specific configuration.

## Source excerpt

As I was doing the final integration tests for netlab release 1.9.0, I stumbled upon a fascinating BGP configuration quirk: where do you configure the allowas-in parameter and why? A Bit of Theory BGP runs over TCP, and all parameters related to the TCP session are configured for a BGP neighbor (IPv4 or IPv6 address). That includes the source interface, local AS number (it's advertised in the per-session OPEN message that negotiates the address families), MD5 password (it uses MD5 checksum of TCP packets), GTSM (it uses the IP TTL field), or EBGP multihop (it increases the IP TTL field). Read more ...