Subject: RE: Active Route

From: "Natale, Jonathan" <[email-masked]>
Date: Wed, 2 Oct 2002 11:32:50 -0400

Christian,

Thank you for replying.

Your change would not cover the case, for example, where the speaker
uses a static route that is not redistributed into bgp to reach
a set of destinations that is also learned via bgp.

I was thinking of:
"one must focus on the rule that a BGP speaker advertises to 
its peers only routes whose set of destinations
are reachable per the local Routing Table."

-----Original Message-----
From: Martin, Christian [mailto:[email-masked]] 
Sent: Wednesday, October 02, 2002 10:28 AM
To: 'Natale, Jonathan'; [email-masked]
Subject: RE: Active Route

Jonathan,

>
>"one must focus on the rule that a BGP speaker advertises to 
>its peers (other BGP speakers which it communicates with) in 
>neighboring ASs only those routes that it itself uses."
>
>This means that if the speaker's routing table has a non-bgp 
>route to a destination but does not have bgp route to the same 
>destination (for example, based on administrative distance), 
>then the speaker may not advertise that route to it's peers. 
>This is true on Juniper by default for EBGP, but is NOT TRUE 
>[ever?] on Juniper for IBGP, and is NOT TRUE on Juniper if ~= 
>"advertise inactive" is enabled.  This is NOT TRUE ever on Cisco.
>
>Now we are proposing that the quoted clause above be 
>completely removed. This means that it will be allowable to 
>advertise a route to a destination that is not locally 
>reachable.  This is obviously (to me, but not to all-- which 
>is why it should not be removed) bad. 

This, IMO, is not the spirit of the rule.  Juniper interpreted the spec
differently.  As I see it, if the route is in the routing table, you can
announce it.  To be more specific, and to your point Jonathan, we should say
this - or say the converse:

"one must focus on the rule that a BGP speaker advertises to 
its peers (other BGP speakers which it communicates with) in 
neighboring ASs only those routes learned via BGP that it 
itself uses.  "Learned via BGP" means that a router's best path
to a prefix is one that was either learned from a BGP peer, or
deliberately injected into BGP by the local router."

Regards,
-chris

>Thank you.

---

From: "Michael C. Cambria" <[email-masked]>
Date: Wed, 02 Oct 2002 11:49:27 -0400

> deliberately injected into BGP by the local router."

to the text below work (removing the "best path" reference)?

"one must focus on the rule that a BGP speaker advertises to
its peers (other BGP speakers which it communicates with) in
neighboring ASs only those routes learned via BGP that it
itself uses.  "Learned via BGP" means that the route to be
advertised is one that was either learned from a BGP peer, or
deliberately injected into BGP by the local router."

This calls out that a speaker can't advertise a route to
neighboring ASs that are not known to BGP.  Yet it does not preclude a 
route known to BGP from being advertised that has either the destinaiton 
or the NEXT_HOP (or both) reachable in the routing table via an IGP 
route (e.g. due to admin distance) as required by 9.1.3:

"A route shall not be installed in the Adj-Rib-Out unless the 
destination and NEXT_HOP described by this route may be forwarded 
appropriately by the Routing Table."

fire away :-)

MikeC