Hello Christian,
thanks for reply! Maybe I do not see some obvious solution with MED...
The point is, that I need to route traffic from all of my upstreams to
my customer AS2 via one path and any other traffic from my AS or from my
other customers via another path facing AS2 too. So the problem is not
which of two routes with the same prefix and different next-hops should
be installed into routing table - that is, what the MED solves, AFAIK.
The problem is how to use concurrently on a one single box two routes
with the same prefix and different next-hops and select which of routes
is to be used based on where the traffic comes from (not src IP address
but interface).
Tomas
Christian Koch wrote:
use meds
On Sun, Sep 14, 2008 at 5:48 PM, Tomas Hlavacek
<[EMAIL PROTECTED]> wrote:
Greetings!
I am thinking about a scenario, which is maybe quite common, but I do not
know how to make that work.
Say that an AS1 is receiving full BGP table from multiple upstreams, for
example AS100 and AS200. AS1 has a customer, say AS2. There is one Ethernet
physical connection between border routers of AS1 and AS2. AS2 is paying to
AS1 for upstream and receives full BGP feed. AS1 has another customer AS3,
paying for upstream also. Besides that AS1 and AS2 has a peering via some
IX. AS2 is stub, so it is announcing only prefixes with as-path ^2$. AS1 is
announcing ^1$ and ^1 3$ prefixes to its peers in the IX. AS1 preferres
paths via IX by local-preferrence.
The point is how to make packets traveling from upstreams of AS1 to AS2 not
to take path via IX, but via direct Ethernet connection while traffic
originating in AS1 and traffic from AS3 traveling trough AS1 take path via
IX?
I have two ideas:
1) policy based routing, bind some route-map to AS1's upstream-facing
interfaces and set ip next-hop or set interface... But it does not scale
well of course.
2) put transit neighbors (upstream and customers also) into vrf, for
example:
ip vrf transit
rd 1:100
export map EXPORT_ALL
import map IMPORT_ALL
!
router bgp 1
network 1.1.1.0 mask 255.255.255.0
neighbor 2.2.2.1 remote-as 2
neighbor 2.2.2.1 route-map SET_IX_LOCPREF in
neighbor 2.2.2.1 filter-list 1
!
address-family ipv4 vrf transit
neighbor 1.1.0.1 remote-as 100
neighbor 1.1.0.1 route-map SET_TRANSIT_LOCPREF in
neighbor 1.1.0.1 description UPSTREAM1
neighbor 1.1.0.2 remote-as 200
neighbor 1.1.0.2 route-map SET_TRANSIT_LOCPREF in
neighbor 1.1.0.2 description UPSTREAM2
neighbor 2.2.2.2 remote-as 2
neighbor 2.2.2.2 route-map SET_TRANSIT_LOCPREF in
neighbor 2.2.2.2 description CUSTOMER AS2
neighbor 3.3.3.1 remote-as 3
neighbor 3.3.3.1 route-map SET_TRANSIT_LOCPREF in
neighbor 3.3.3.1 description CUSTOMER AS3
!
!
route-map SET_IX_LOCPREF permit 10
set local-preference 200
!
route-map SET_TRANSIT_LOCPREF permit 10
set local-preference 100
!
route-map EXPORT_ALL permit 10
!
route-map IMPORT_ALL permit 10
!
I spent few hours in lab experimenting with this configuration. I am using
old Cisco 1600, so there is possibility that issues I had could come from
some bug in this EoL platform... For reference, I used IOS (tm) 1600
Software (C1600-SY-M), Version 12.2(37) RELEASE SOFTWARE (fc1) for
experiments. Problems:
1) routes in vrf transit are learned to into vrf routing table and are
announced in both directions from AS100 to AS2 and AS3 and vice-versa, as
expected. But routes from vrf transit are not exported into global routing
table nor imported from global into vrf. I tried everything (I put some
prefix- or access-list to match ip address clause in IMPORT_ALL and
EXPORT_ALL maps,...), but nothing appeared in the global table. It should be
some misconfiguration over there but I do not see that. Any help would be
appreciated.
2) Let's assume that the import and export works, so I have all transit
routes in my global table and route 1.1.1.0/24 inside vrf transit (this is a
route originated in AS2). Those routes are therefore in fact duplicated...
Is there any mechanism or chance to overcome that? Something like default
route in global table pointing into transit VRF and triggering one extra
routing decission inside VRF? Or is the duplication somehow optimized and it
won't be any problem even for full BGP table? (O course I mean full table on
real routers... 7200 or 7600.)
Is there any best-practice or common approach to that? Maybe something
completly different which I am not aware of?
Tomas
--
Tomáš Hlaváček <[EMAIL PROTECTED]>
_______________________________________________
cisco-nsp mailing list cisco-nsp@puck.nether.net
https://puck.nether.net/mailman/listinfo/cisco-nsp
archive at http://puck.nether.net/pipermail/cisco-nsp/
--
Tomáš Hlaváček <[EMAIL PROTECTED]>
_______________________________________________
cisco-nsp mailing list cisco-nsp@puck.nether.net
https://puck.nether.net/mailman/listinfo/cisco-nsp
archive at http://puck.nether.net/pipermail/cisco-nsp/
