HSRP config

Unanswered Question
May 22nd, 2009

Folks

We are planning for redundancy setup between 2 sites.Attached the router setup bw sites.

Can let me know if HSRP can be configured between R1 and R3.If so,how ?

SAM

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crow930us Fri, 05/22/2009 - 07:34

HSRP support for Multiprotocol Label Switching Virtual Private Networks (MPLS VPNs) was added in Cisco IOS release 12.1(3)T.

HSRP on an MPLS VPN interface is useful when you have an Ethernet connected between two Provider Edges (PEs) and you have either of the following:

* A Customer Edge (CE) with a default route to the HSRP virtual IP address.

* One or more hosts with the HSRP virtual IP address configured as the default gateway.

This tech note should have more info: http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094a91.shtml#hsrpsupport

sarsamivel Sun, 05/24/2009 - 06:30

I shud hav given more info on the setup.

R1 and R3 are managed by service providers.R2 and R4 are managed by customer.

R1,R2 in Site A and R3,R4 in site B.

currently R1 and R2 are in HSRP and same as R3 and R4.

Now we wanted to utilize both MPLS links at site A and B for Site A traffic.like Active-Active setup,same time need redundancy in setup.How can we acehieve this?

let me know if more info needed.

Thanks in advance

SAM

Giuseppe Larosa Sun, 05/24/2009 - 11:46

Hello Sam,

if multiple hosts are present in each client vlan you can use GLBP.

see

http://www.cisco.com/en/US/docs/ios/ipapp/configuration/guide/ipapp_glbp_ps6350_TSD_Products_Configuration_Guide_Chapter.html

the requirement is that all devices have to be Cisco devices because it is a proprietary protocol.

if the device in the client is only one you can use multiple HSRP groups and you can double each static route using as IP next hops the two VIPs

tracking of interfaces or using ip sla objects is possible with both protocols and completes the solution (preemption is needed )

Hope to help

Giuseppe

sarsamivel Sun, 05/24/2009 - 20:45

Hi Giuseppe,

Is it possible to configure MHSRP on R1 and R3 in ths scenario and provide redundancy as well load balancing.

I know HSRP works on ethernet,will i be able to bring R1 and R3 in same LAN ?

Thanks

SAM

Giuseppe Larosa Sun, 05/24/2009 - 22:00

Hello Sam,

R1 and R3 are the routers under your control but they are in different sites.

the proposal is for routers on the same site: you should coordinate the changes with who manages R2 and R4 in order to achieve load balancing for traffic between the two sites (both directions)

Without involving the people who manages R2 and R4 there is little you can do: you can have R1 and R3 active routers for the existing HSRP group but this is not enough to achieve load balancing.

Hope to help

Giuseppe

sarsamivel Sun, 05/24/2009 - 23:18

Hi Giuseppe,

If i have 2 equal cost routes to same destination,to what extent i can acheive loadbalacing?

What changes i need to make at other end?I have to configure two equal cost route via two links back to the source,is tht right ?

Thanks

SAM

Giuseppe Larosa Mon, 05/25/2009 - 02:21

Hello Sam,

your understanding is correct

to achieve load-balancing you need two equal cost paths.

on both directions = on both sites

for end users GLBP provides load balancing at the ARP level.

the right tool to use depends on your scenario details.

Hope to help

Giuseppe

sarsamivel Mon, 05/25/2009 - 03:44

Hi Giuseppe,

Thanks for guiding me.one more question.

How does equal cost path routes perform load balancing?Can we acheive perfect load balance b/w two links.?

SAM

Giuseppe Larosa Mon, 05/25/2009 - 05:48

Hello Sam,

once there two paths installed in the routing table CEF performs load balancing.

Standard CEF load balancing is per flow

the two paths are logically numbered 0 and 1

(IP SA last bit) Exor (IP DA last bit) Exor Hash_seed

provides a 0 or 1

flows with IP SA and DA that gives result 0 are sent out path 0, flows whose IP SA and DA gives result 1 are sent out path 1.

If your traffic is enough variable: it is made of many low volume traffic flows the balancing results are good.

if there is a single very high volume flow (example a DB synchronization) all packets of the flow use a single link

Hope to help

Giuseppe

sarsamivel Mon, 05/25/2009 - 06:18

Hi Giuseppe,

Will the return traffic will use the same path per flow.

by FLOW,i understand it's a TCP session ?

We will have only RDP,Telnet and Management traffic on these links.Shud there be an issue on latency?

Thanks,

SAM

Giuseppe Larosa Mon, 05/25/2009 - 07:16

Hello Sam,

no each device choices how to send packets so it is possible that return traffic takes the other path.

A flow is direction specific for CEF forwarding purposes.

Hope to help

Giuseppe

sarsamivel Mon, 05/25/2009 - 08:06

Hi Giuseppe,

Based on your experiences do you see any issues for Management protocols like telnet,RDP etc when the response comes thru second link.This link will have additional latency of 10ms to the site.

Thanks

SAM

Giuseppe Larosa Mon, 05/25/2009 - 08:43

Hello Sam,

I don't think this delay difference (10 ms) can be an issue for Telnet or RDP and other TCP based applications.

Hope to help

Giuseppe

rakesh.hegde Mon, 05/25/2009 - 10:59

Hi Giuseppe ,

During load balancing paths for a prefix are assigned internally to 16 hash buckets in a round robin pattern right ? The result of the hash function based on source and destination ip (value between 0-15) is used as a pointer to pick one out of 16, and thus which path to use for the flow.

See link below

http://www.cisco.com/en/US/tech/tk827/tk831/technologies_tech_note09186a0080094806.shtml

Please let me know if I am missing something .

-Rakesh

sarsamivel Mon, 05/25/2009 - 22:47

Hi Giuseppe,

Does the load balancing mechanism is same in cisco ASA also?

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