hi Mohamed

the lo0 of both bgp peers advertised thorugh ospf

and reachable through the IGP

but there are som other lo interfaces advertised thorugh bgp

its shown in the bgp table but as not advertised

and showing the next hope ( the other peer lo0) as inaccessable

i would say without ttl 3 no peer will be established as t is not directlyu connected EBGP peers

as i mentioned this topolog works fine if i use ebgp-multihope command instead of ttl security

is it more clear now

i found it strange

Hello Marwan,

the TTL security mechanism should tell what is the expected TTL on received BGP packet from peer to consider it valid.

see

http://www.cisco.com/en/US/docs/ios/iproute/configuration/guide/irp_bgp_neighor_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1054684

I think you should use both commands if these are eBGP sessions

Hope to help

Giuseppe

hi Gusseppe

according to this linke which i seen it before

The neighbor ebgp-multihop command is not needed when this feature is configured for a multihop neighbor session and should be disabled before configuring this feature

so we can NOT use both of them

try it

when you have ebgp-multi

and you enter the ttl command it will give error messege tell you you can't have both of them !!!

thats why i found it strange becuase in term of TTL in and out all good thats why i got my peering seesion up

but why it tells next hop in accessable

i still wonderring

anyway thank you for your time

Hello Marwan,

I've realized later I had suggested a wrong idea.

you should verify if:

the BGP next-hop of routes is known in routing table.

this is the standard check and this has to be there.

I wonder what additional checks can be done enabling ttl-security on BGP next-hop.

looking for the number of route-hops to next-hop would require a traceroute and it is unlikely.

Hope to help

Giuseppe