Access to default gateway

Answered Question
Sep 22nd, 2011

Hi.

Screen.png

I have router (cisco 2811), 2 switches and client. I want that client has one default gateway to 2811 (for example gateway ip will be up on Loopback interface) and if one of the links from switch to gateway down, gateway ip will be available. I don't know how to do it, can u help me?

I have this problem too.
0 votes
Correct Answer by Talha Ansari about 2 years 7 months ago

Hi Maxim,

I think I get what you are trying to achieve. You want just one IP address as a default gateway which should be available from your client with redundancy between two fast-ethernet ports of your 2800 router. However it would be best to have two routers at your gateway and have HSRP between them.

As your current situation goes I think you could have one possible solution(or could be more which I could not think at this moment)...

1) You can configure a BVI interface and associate both the ethernet interfaces to that group. These two interfaces of the router would a part of the spanning-tree instance and one would be forwarding and another in blocking state. You need to have trunk between two 2960. Make sure both the router's fastethernet ports are in same VLAN on the 2960 switch.


On 2800

bridge irb
bridge 10 protocol ieee
bridge 10 route ip


int bvi 10
ip address x.x.x.x x.x.x.x


int fas 0/0
no ip addr
bridge-group 10

int fas 0/1
no ip addr
bridge-group 10

Here if one port of the router goes down the other port would become forwarding. Note that convergence time from blocking to forwarding on your router could be 50 seconds.

You may check the following show command on your 2800

sh spanning-tree 10

HTH

Talha

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Cadet Alain Thu, 09/22/2011 - 05:34

Hi,

You could simply let spanning tree do the job for you.

Decide the root bridge with spanning-tree vlan x priority Y  command and in case of failure spanning-tree will reconverge.If you configure Rapid spanning-tree it will only take a few seconds.

Regards.

Alain.

ieasm0001 Thu, 09/22/2011 - 06:03

I think u don't understand me:) Sorry for my english.

I create the Loopback interface on my router, which connected to 2 switchs. I want that this loopback will be gateway for client. If link between switch port  and router goes down, loopback will be available from other interface. How can i do it?

Cadet Alain Thu, 09/22/2011 - 06:34

Hi ,

As I said above.

if Your switches are L2 then you can traffic engineer the L2 path with PVST+ or RPVST+.

L3 is using L2 to encapsulate so the L3 traffic will follow L2 path.

Regards.

Alain.

ieasm0001 Thu, 09/22/2011 - 22:55

How client will ping gateway? If i up 2 private networks between router  and client, then client can ping gateway(Loopback), usng static routes or, for example, ibgp. But maybe u know better  way to let client ping gateway. Maybe u know how to configure route-map for this situation or something else.

Correct Answer
Talha Ansari Thu, 09/22/2011 - 23:50

Hi Maxim,

I think I get what you are trying to achieve. You want just one IP address as a default gateway which should be available from your client with redundancy between two fast-ethernet ports of your 2800 router. However it would be best to have two routers at your gateway and have HSRP between them.

As your current situation goes I think you could have one possible solution(or could be more which I could not think at this moment)...

1) You can configure a BVI interface and associate both the ethernet interfaces to that group. These two interfaces of the router would a part of the spanning-tree instance and one would be forwarding and another in blocking state. You need to have trunk between two 2960. Make sure both the router's fastethernet ports are in same VLAN on the 2960 switch.


On 2800

bridge irb
bridge 10 protocol ieee
bridge 10 route ip


int bvi 10
ip address x.x.x.x x.x.x.x


int fas 0/0
no ip addr
bridge-group 10

int fas 0/1
no ip addr
bridge-group 10

Here if one port of the router goes down the other port would become forwarding. Note that convergence time from blocking to forwarding on your router could be 50 seconds.

You may check the following show command on your 2800

sh spanning-tree 10

HTH

Talha

Cadet Alain Fri, 09/23/2011 - 01:19

Hi Talha,

I had forgotten the gateway was a router not a L3 switch indeed so i think your solution is indeed the correct one.

Regards.

Alain.

Talha Ansari Fri, 09/23/2011 - 03:08

Hi,

Well you may achieve your goal by the BVI config for now but it may not be advantageous in long run.

Just for example consider that in future you add another subnet in your network and you need the same 2800 router to be the gateway. In that case you dont have any other ethernet port left in the router which could be configured with an IP address of another subnet. Offcourse you may add a secondary IP address on the BVI itself and use it as a gateway but on the switch side you would need two subnets to be a part of one VLAN which is absolutely not a good idea.... even though this would work too...!

Two routers with HSRP is the best bet.... yet if not two routers then you could insert a HWIC-4ESW card on 2811 then two trunk links could be connected from the router's HWIC-4ESW card to two switches and the BVI interfaces could be replaced by SVI interfaces... and more subnets could be added with link redundancy acquired... I think maximum SVIs supported by HWIC-4ESW is 15.

Talha

ieasm0001 Fri, 09/23/2011 - 05:45

But i can create subinterface on my router and create bvi int on subinterfaces I have already done it and it works.

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Posted September 22, 2011 at 5:10 AM
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