The router looks at the address of the neighbor who sent the BGP advertisement and from the address of the neighbor it knows the AS number of the neighbor. If the AS number of the neighbor is the same as the AS number of the router receiving the update then it is IBGP and the router should not forward the update.
While the update packet does have a TTL, the decision about whether to forward or not does not consider the TTL.
a router keeps track of what advertisements are received by each of its peer.
That is the input RIB.
In building the updates for another iBGP peer all advertisements learned from another iBGP peer are filtered, unless there is a scenario with BGP route reflectors as explained in my first post.
There is no single field in the update message by itself that tells this: in the open message the two devices agree on building an iBGP session because the AS number is the same.
So peers are classified as iBGP peers or eBGP peers when the session is established.
It is built in in the logic of iBGP not an attribute in the update for the possible lack of information that could lead to routing loops (without the additional attributes used by BGP route reflectors or by BGP confederations)
This is actually a pretty cool feature, i didn't even know it existed until I was looking for a solution to advertise a subnet (prefix in BGP talk), only if a certain condition existed. This is exactly what conditional advertisements does
j ai une question j ai achete un routeur cisco 887VA-k9 , je le configuré avec la configuration ci- dessous
si je le lier avec mon pc portable sur l un de ses ports directement ça marche toute est bien ( la connexion internet + m...
Attached policy provides CLI access to the Cisco 4G router over text messaging. Two files are in the attached .tar file:
2. PDF with instructions on how to load and use the .tcl file.