Specifying IP traffic flow using route-maps

[nathan.dixon]

Hi,

I have 2 routers at a customer’s site connecting via 2 serial links to our 2 wan routers. They act as an A and B link. At the customers end we have two FE interfaces, connecting to two LANs. Two instances (one per LAN) of HSRP run on the 2 routers at the customer site. We are running OSPF. On one LAN there is a multicast real-time application server and on the other LAN is an FTP client. We want to force the multicast traffic over the A link with option to run over the B link if the A fails. We also want to force the other 'general LAN' traffic including FTP over the B link only. The sum of the required FTP bandwidth plus the multicast is bigger than the 2Mb serial link so we therefore want the multicast traffic to take priority over the FTP if the A link were to fail.

I have had a look at an existing configuration which only half works. Due to our addressing scheme and PIM, all multicast traffic currently flows over the B links. The OSPF cost of the serial interface has now been lifted from 50 to 100 on the B side. All traffic now flows over the A link.

A route map has been defined on the serial interface of the A router to edit the cost of the FTP LAN traffic with +500. This doesn't work properly, all traffic still flows over the A. After reading up on this it seems 'set metric +500' is only any good when re-distributing between protocols.

What’s the most suitable way for me to make this work well?

It seems I need to do 2 things;

1. Produce a QOS policy on both A and B routers to prioritise multicast over FTP and other management traffic.

2. Produce a route map to make FTP LAN traffic prefer the B side.

I can hopefully produce a QOS policy with little problem.

Shall I move the policy map from the A to the B router and specify the outgoing interface. "set interface s0/0"? Is it correct that I should apply the route policy to the incoming interface (fa0/1)?

Any help much appreciated.

Thanks.

[t.baranski]

If I'm reading your message correctly, I think you can do everything you need to do with policy routing except for the "so we therefore want the multicast traffic to take priority over the FTP if the A link were to fail" part. Policy routing decisions are made on the inbound interface, so you'll want your route-map to be applied on the Ethernet side. And I'd recommend having the route-map point out the serial interface (rather than an Ethernet interface)either via "set interface" or "set ip next-hop". The reason is that you want the router to be able to react when its serial interface goes down. If a policy route-map points out a down interface, the traffic will be forwarded via normal destination-based routing (presumably out the Ethernet interface to the other local router in your case). This gets more difficult if a route-map points out an Ethernet interface, as for all intents and purposes the Ethernet interface isn't going to go down unless the cable is unplugged or the neighboring device is powered down.

[mschooley]

which path is your multicast traffic taking,pim sparse or dense, what interface is seen as rpf interface on routers. if wrong route is being seen as rpf interface, try static mroute back to source pointing to desired interface, however, not sure how to accomplish failover.

[prafuljaded]

Your scenario would have been much simpler if you had a single router at the customer place.But now you need to configure QoS or queueing on both the routers.

10.1.1.0/24--e0--RA--s0------

|

|

10.2.2.0/24--e1----

10.1.1.0/24--e0--RB--s0------

|

|

10.2.2.0/24--e1---

Assume 10.1.1.1/24 is your Multicast Server and 10.2.2.0/24 is your FTP client subnet.Let RB be the HSRP active router for FTP and RA be for Multicast.

RA

int e0

standby 2 ip 10.1.1.1

standby 2 priority 105

standby 2 preempt

standby 2 track s0

int e1

standby 3 ip 10.2.2.1

standby 3 preempt

standby 3 track s0

RB

int e0

standby 2 ip 10.1.1.1

standby 2 preempt

standby 2 track s0

int e1

standby 3 ip 10.2.2.1

standby 3 priority 105

standby 3 preempt

standby 3 track s0

RA and RB:

priority-list 1 protocol ip high list 10

access-list 10 permit host 10.1.1.1

int s0

priority-group 1

Hope that helps