Routing between Router and L3 switch

Unanswered Question
Jun 22nd, 2010

Hello Everyone,

                      I am facing problem in routing between Router and L3 switch. In our network there is core Router, which is connected with L2 switch and then L2 switch is connected with  L3 switch and then L3 switch is connected with ISA server which have two interface one is Public and another is Private. The private interface is directly connected with L3 switch and Public interface is connected with L2 switch. Here in our network Traffic coming in to core router from various sites for the internet that  traffic is shifted to L3 switch using route maps. When the traffic reachs towards L3 switch here we have made default route which tells anything which comes in L3 switch is shifted to ISA server here in ISA server all the traffic is going outside with using Pubilc IP. Now when the traffic is coming back after coming outside the path is first router then ISA server here in ISA server there is a Persistent Routes which tells the ISA server if any traffic will come back shift it to L3 swicth. Then in L3 switch we are using ospf so all the traffic is going to router by ospf. Now what i want i want to remove ospf in L3 switch and i want to send traffic with static route. Please Help me out from this probem.

I have this problem too.
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Giuseppe Larosa Tue, 06/22/2010 - 21:44

Hello Jaral,

if the router and the L3 switch are not directly connected and there is the L2 switch in the middle, you need to use a dynamic routing protocol or the devices will not be able to detect a failure.

So I recommend you to stay with OSPF. You can consider to use EIGRP if you wish to perform some route filtering per interface.

Otherwise you would discover that if the static route IP next-hop fails, the static route is not removed until the ARP entry for the next-hop is in ARP table and with default timers it means up to 4 hours !!!

You would need to use IP SLA to monitor the state of ip next-hop but at this point using a dynamic routing protocol is the easier choice as the routing protocol hellos will be your IP SLA.

Hope to help

Giuseppe

dimplejaral Tue, 06/22/2010 - 23:22

Hello sir,

            Can i create route map in L3 switch which tells when the trafic will come for my ISA server in to L3 switch, send that traffic to my router, plz see the below conf and guide if there is any change..

access-list 101 permit ip any ( My whole Lan segmant )

route-map test permit 101

match ip address test

set ip next hop ( My router address )

and then

interface gig1/0/23

ip policy route-map test

this interface is connected with ISA server private lan card..

Giuseppe Larosa Tue, 06/22/2010 - 23:31

Hello Jaral,

generally speaking the answer is yes you can use policy based routing on multilayer switches and PBR  implementation is efficient on them.

What is important to consider is that PBR acts inbound on received traffic on an interface

To understand if you need PBR or not in your scenario you should attach a jpeg file with a network diagram it is difficult to understand if it is needed or not.

Also using PBR for all traffic as in your example is not meaningful.

so provide a network diagram if you can.

if you use OSPF between the L3 switch and the router you may be already ok or not

if it is :

core router ------ L3 switch ---- ISA --- public address ----internet

OSPF routes can be used to send traffic to internal destinations with no problems.

A default route pointing to ISA server can be used for traffic with an internet destination.

the L3 switch can generate a default route in OSPF using default-information originate command in router ospf context

L3 switch:

ip route 0.0.0.0 0.0.0.0

router ospf 10

default-information originate

the ISA needs static routes for the internal networks pointing  to L3 switch ip address in the link they share

unless there is another exit to the internet and some traffic has to bypass the ISA I don't see any need for PBR but I may be wrong as I don't know the details of your scenario.

Hope to help

Giuseppe

dimplejaral Wed, 06/23/2010 - 00:15

Hello Sir,

          I am sending my network daigram which will help you to know about my problem, here in my dai there is router, L2 switch, ISA server and L3 switch. All the sites traffic request for internet  is coming on router and then router is sending all the traffic to L3 switch by route map and then L3 sending this traffic to ISA server and now using public ip ISA server is sending that traffic to router and hence the traffic is going outside see the case when traffic is coming back from outside here the traffic is coming to router then router is forwading that traffic to ISA server, here in ISA server there is route which is saying send all the traffic to L3 switch, now all the traffic is in L3 switch here we are using ospf so that L3 communicate with router and the users will reacive the internet request..What i want to do, i want to remove ospf in L3 switch and i want to use static routing in L3 switch.....Hope you will understand my Problem......

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