Clearing Up Some Misinformation RE: eBGP Multihop and TTL
Myth: You have to set ttl to 2 because it is decremented on the way to the loopback.
**This blog is a formatting cleanup and update to a previous blog I posted in 2013 on NetworkWorld.
Years and years ago I was trying to learn more about BGP and I was reading some book with a chapter on the topic. Back then I pretty much believed that if it made it into a book it must be true and my knowledge had to be in error. So to say I was confused back then would be an understatement.
Why? Well ya see… they basically said that the reason one must set the TTL to 2 for eBGP peers that are directly connected, but peering with their loopbacks, was cause “the TTL gets decremented on the way to the loopback”
When I try to help someone deprogram this brain washing, I find pictures help. So for those who’d like to get deprogrammed and learn the truth… Let’s go play in the lab!!!
In the picture above we have 3 Routers in 3 different BGP ASes. We all probably know that if we peer R1 and R2 Continue reading