2 gateways of last resort

Answered Question

What will happend if two gateways of last resort is configured on a 6509?

ip route 0.0.0.0 0.0.0.0 172.16.24.1

ip route 0.0.0.0 0.0.0.0 172.31.14.254

Will the 6509 going to pick 172.16.24.1 or is it going to load balance between the 2 ?

TIA

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Faizan Shaikh Thu, 04/15/2010 - 11:36

Jon,

Is it going to play round-robin for these two static routes?

If yes, how does it actually happen?

is it session based or something?

Regards,

Faizan

Jon Marshall Thu, 04/15/2010 - 11:40

fisi1232000 wrote:

Jon,

Is it going to play round-robin for these two static routes?

If yes, how does it actually happen?

is it session based or something?

Regards,

Faizan

Faizan

Yes it will and it does it based on destination address.

Jon

Jon Marshall Thu, 04/15/2010 - 12:03

fisi1232000 wrote:

Jon,

"based on destination address"

Can you please elaborate this in brief ?

There are 2 types of load-balancing , per-packet and per-destination.

Per-packet means each packet is routed separately so with 2 default routes each new packet would be sent over alternate default routes.

Per-destination means each packet that is going to the same destination is sent over the same path using the same default route.

Have a look at this doc for more details -

http://www.cisco.com/en/US/customer/tech/tk365/technologies_tech_note09186a0080094820.shtml#perper

Edit - should have mentioned that on a 6500 with sup720 only per-destination load-balancing is supported.

Jon

Faizan Shaikh Thu, 04/15/2010 - 12:12

Jon,

Okay, good.

It means for 'per packet', same packet will go through two default routes.

and 'per destination' means one packet one destination.

Regards,

Faizan

Jon Marshall Thu, 04/15/2010 - 12:23

fisi1232000 wrote:

Jon,

Okay, good.

It means for 'per packet', same packet will go through two default routes.

and 'per destination' means one packet one destination.

Regards,

Faizan

Faizan

The same packet cannot go through 2 default routes. per-packet means packet 1  is sent over default-route1, packet 2 is sent over default-route2, packet 3 is sent over default-route1, packet 4 is sent over default-route2 etc....

per destination means any packet with the same destination IP address in the IP header is sent over the same default-route.

Jon

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