Re: : Can a prefix be never routed on Internet but used only for source address in IP packets?

[Nick Hilliard via NANOG <nanog () lists nanog org>]

nanog--- via NANOG wrote on 20/08/2025 04:10:
> I believe IXP networks are usually like this. Globally assigned IPs,
> and routers can use their IPs on the network to originate ICMP
> packets (e.g. TTL exceeded during traceroute; or packet too big) but
> putting a route to the IXP network on the internet is strictly
> prohibited.
There's no prohibition here. It's an issue for the IXP's routing policy 
as to whether their peering lan prefix(es) should be announced or not. 
Some do, many don't.

The thing that IXPs don't like is when second or third parties become 
inventive in ways that override the intention of the IXP, for example, 
originating the address block from their own ASN, or putting in 
special-case filters to single out ixp prefixes for special treatment, 
or that sort of thing. It would also help if connected parties used 
next-hop-self at their IXP routers so that peering lan prefixes are not 
carried in their IGPs.

Nick
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