Question about redundancy between SM-SRE in two routers

[gwhuang5398]

I have two 2921 routers at the remote site, each has a SM-SRE-700 module installed to run WAAS. Is it possible to have redundancy between the two modules in two routers? how to have the two modules form a farm wit each 2921 router?

I also have a large site with two ASR1002 routers, each connects to a WAE-7341 appliance. Is there anything I need to be aware in particular betwen ASR and WAE configurations? I looked up Cisco documents but didn't find right information. Can I just use the general configuration on the ASR routers as other ISR routers?

Thanks a lot

Gary

[tkumarag]

Hi Gary

Technically as far as IP reachability is there among the routers and SREs, they should be able to form a farm. Also hope you aware that this solution won't be able to give the same redundancy as isolated platforms, ie: when router fails, SRE also goes down. However I'll let other experts to comment on their recomendation on this..

Following document is a good one to understand WCCP on ASR100) which is the key area you need to focus when integrating with WAAS

Deploying and Troubleshooting Web Cache Control Protocol Version 2 on Cisco ASR 1000 Series Aggregation Services Routers

http://www.cisco.com/en/US/prod/collateral/routers/ps9343/white_paper_c11_502351.html

thanks

Thusi

[Bhavin Yadav]

Hi Gary,

I agree with Thusi. As far as ip connectivity is good, WAE is good incase of mobules.

You can add both 2921 and oth SMSRE modules in one WCCP farm and do the load sharing. Please also think about using egress method option if you are using WCCP to avoid Asymmetrci routing. More details here:

http://www-europe.cisco.com/en/US/prod/collateral/contnetw/ps5680/ps6870/prod_white_paper0900aecd806d976a_ps6474_Products_White_Paper.html

IP Forwarding Egress Method and Supported Cisco WAE Deployment Scenarios

When  the IP forwarding egress method is used, the return traffic packets are  forwarded to the Cisco WAE default gateway. IP forwarding is the  default egress method Cisco WAE uses to return redirected traffic, and  it is part of the Cisco WAE default configuration. With the IP  forwarding egress method, the Cisco WAE must be deployed on a separate  subnet from users and servers, which can be accomplished using  subinterfaces or tertiary interfaces (Figure 1). The command-line  interface (CLI) command to configure IP forwarding as the egress method  is shown here:

WAE(config)# egress-method ip-forwarding intercept-method wccp

Figure 1. Limitation of IP Forwarding: Cisco WAE Must Reside on a Separate Subnet to Prevent Infinite Forwarding Loop

When  using the GRE egress method, the return traffic packets are returned  back to the intercepting router using the GRE tunnel that is created as a  result of WCCP negotiation. With the GRE return egress method, the  Cisco WAE can be deployed on the same subnet as users or servers, and  subinterfaces or tertiary interfaces are not required (Figure 2). The  CLI command to configure GRE return as the egress method is shown here:

WAE(config)# egress-method negotiated-return intercept-method wccp

Further few more things you want to keep in mind.

1. There is no active redundancy (tcp session replication) between WAAS. The connection that initiates from WAE1 has to come back to WAE1 to optimize otherwise it will create Asymmetric routing.

About ASR 1002 routers and WAE-7341 WAEs, there are no known issues and they should work fine with L2/Mask with redirect IN options.

Hope this helps.

PS: Please mark this as Answered, if this answers your question.

[gwhuang5398]

Thanks both of you very much for the advices. For ASR-1002 working with WAE appliances, the Layer 3 redirection/return configuration would be no different from other ISR routers. I have heard, and you mentioned too, that ASR router can also do L2 redirection with WAE appliances. I'm not clear how that is done because that requires ASR router and WAE Layer 2 adjacent. Is there a sample deployment or configuration that I can reference?

For the redundancy between SM-SRE modules in 2 different routers, I was thinking about this scenario: if one module goes bad, its router could redirect traffic to the module in the other router. Redundancy may not be the right word for it. Here is the router connectivity:

ISR A has a SM-SRE (module A) running WAAS;

ISR B has a SM-SRE (module B) running WAAS;

Both ISR A and B connect to the aggregation switch (could be Layer 2 or Layer 3 switch).

Each module has IP reachability to either router with no problem. If I list both routers in module's WCCP router list, the two modules would form a farm and known by both routers. In that case, would it be possible that ISR A does load balancing between the two modules and direct some traffic to the module in ISR B? That would be undesired.

For asymmetric routing, negotiated return can provide a good solution. However for modules which is directly connected to the router internally, the negotiated GRE return would add additional tunneling overhead. Have you seen real deployment like that?

Thanks again

Gary

[Bhavin Yadav]

Hi Gary,

Answers to your questions:

Is there a sample deployment or configuration that I can  reference?

Ans: Yes, this is possible nad can be done. You probably want to discuss this with your Cisco Sales team to get such sample configurations or scenarios as they go thru tkind of exercise everyday.

For  the redundancy between SM-SRE modules in 2 different routers, I was  thinking about this scenario: if one module goes bad, its router could  redirect traffic to the module in the other router. Redundancy may not  be the right word for it. Here is the router connectivity:

ISR A has a SM-SRE (module A) running WAAS;

ISR B has a SM-SRE (module B) running WAAS;

Both ISR A and B connect to the aggregation switch (could be Layer 2 or Layer 3 switch).

Each  module has IP reachability to either router with no problem. If I list  both routers in module's WCCP router list, the two modules would form a  farm and known by both routers. In that case, would it be possible that  ISR A does load balancing between the two modules and direct some  traffic to the module in ISR B? That would be undesired.

For  asymmetric routing, negotiated return can provide a good solution.  However for modules which is directly connected to the router  internally, the negotiated GRE return would add additional tunneling  overhead. Have you seen real deployment like that?

Ans: Again, I am from Cisco TAC team, you probably want to refer to the Cisco Sales team for this one. They are experts in this sort of designing questions. Someone from PDI helpdesk can also ping in here. But your concern is right about the overhead.