Henry's Points

The water in BGP is deep, I should say. However, to make our world simpler, we may summarize our knowledge by one screen shot. For example, to learn BGP neighbor features, we can simply see what options besides neighbor commands. Let’s take a screen shot first.

I can safely say that, each commands can be one section on the book or tutorials.

• For example, we can change EBGP default TTL=1 to 255 by issue ebgp-multihop command. We also can restrict neighbor hop count by issue ttl-security command.
• allowas-in will be last resort for some AS is partitioned, but it may cause count-to-infinity problem if hop-count is larger.
• when we issue send-community, then we know what’s well-known four communities are.
• local-as is tell neighbor that advertised routes are originated by using this AS number. The AS number will be preapended on the real AS.
• next-hop-self is useful when advertising route to iBGP but the neighbor doesn’t have the route on IGP table. If the iBGP neighbor doesn’t change next-hop value, then it has no way to know how to get that route. next-hop-unchange is useful to solve loop problem when eBGP neighbor set next hop to me and the actual route has to bypass this neighbor.
• max-prefix is another security feature which only allows certain number of TCP session up.
• soft-reconfiguration is good feature to ask neighbor re-advertise route without tear down and resetup TCP session. It’s more like command “clear ip bgp * soft“.
• etc…

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