On Tue, Oct 09, 2001 at 01:19:47PM -0500, Kerry Schwab wrote:
> This is certainly a good suggestion, but it won't work for those
> sites like mine, where the servers are behind a single
> firewall. ( the firewall is an H/A pair, but only one is active at a time).
>
> The firewall doesn't support the idea of multiple default routes, and
> for obvious security reasons, we don't want the firewall to accept
> dynamic routing updates.
>
> I have gone through several ideas, but I'm really more interested
> in whether I can "globally subtract" the last hop count ( the ethernet
> between the two routers) from BGP routes that are exchanged between
> the two routers. I suspect I can't do this, just wanted the confirmation :)
The BGP selection process is a listed below: (From the * URL, couldn't
find a similar document on Juniper's site)
So in the case where you don't change any of the metrics (local-pref,
MED, origin code etc.) and your providers have similar AS path length's
you will prefer a eBGP path over a iBGP path, so my advise would be to
use inbound AS path prepending on the M5 with the active VRRP address,
but that might force most of the traffic onto the other M5, so you will
have to experiment with it.
1. If the next hop is inaccessible, do not consider it.
2. If the path is internal, synchronization is enabled, and the route is
not in the IGP, do not consider the route.
3. Prefer the path with the largest weight (weight is a Cisco
proprietary parameter).
4. If the routes have the same weight, prefer the route with the largest
local preference.
5. If the routes have the same local preference, prefer the route that
was originated by the local router.
6. If the local preference is the same, or if no route was originated by
the local router, prefer the route with the shortest autonomous system
path.
7. If the autonomous system path length is the same, prefer the route
with the lowest origin code (IGP < EGP < INCOMPLETE).
8. If the origin codes are the same, prefer the route with the lowest
Multi Exit Discriminator (MED) metric attribute.
9. Prefer the external (EBGP) path over the internal (IBGP) path.
10. Prefer the route that can be reached through the closest IGP
neighbor (the lowest IGP metric).
11. If the following conditions are all true, insert the route for this
path into the IP routing table:
Both the best route and this route are external.
Both the best route and this route are from the same neighboring
autonomous system. maximum-paths is enabled.
12. If multipath is not enabled, prefer the route with the lowest IP
address value for the BGP router ID.
The router ID is usually the highest IP address on the router or the
loopback (virtual) address, but might be implementation-specific.
*) Ignore weight is's Cisco properitary.
<http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/np1_c/1cprt1/1cbgp.htm#xtocid87022>
/Jesper
-- Jesper Skriver, jesper(at)skriver(dot)dk - CCIE #5456 Work: Network manager @ AS3292 (Tele Danmark DataNetworks) Private: FreeBSD committer @ AS2109 (A much smaller network ;-)One Unix to rule them all, One Resolver to find them, One IP to bring them all and in the zone to bind them.
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