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IP Route Question

I have two data centers and I am starting to look into VPN failover. Will the following scenario cause me to have a routing problems. What exactly will this do.

ip route 5.5.5.5 255.255.255.255 8.8.8.8

ip route 5.5.5.5 255.255.255.255 9.9.9.9

10 REPLIES
Hall of Fame Super Bronze

Re: IP Route Question

No much information to go by, the route you posted will load-balance via links 8.8.8.8 and 9.9.9.9 for traffic going to host 5.5.5.5

HTH,

__

Edison.

New Member

Re: IP Route Question

It should be noticed that link cost matters. Most protocols won't balance over unequal links.

Hall of Fame Super Bronze

Re: IP Route Question

This is an ip route, not a dynamic routing decision. It doesn't care about the cost.

New Member

Re: IP Route Question

right! foolish me, I stand corrected.

New Member

Re: IP Route Question

edio..

please brief a little how that route load balcne the traffic.can we use such a route while forwarding traffic from a single source to two different ISPs ?

Hall of Fame Super Bronze

Re: IP Route Question

It will load-balance the traffic as the destination will have two equal paths in the routing table.

As the packet traverses this routing device destined for host 5.5.5.5, this routing device looks at its routing table and sees there are 2 devices acting as gateway. It will use both gateways proportionally.

One thing to keep in mind is the return traffic. If you don't have similar return path, the traffic may be asymmetrical.

Can you elaborate what you are trying to achieve ?

HTH,

__

Edison.

New Member

Re: IP Route Question

"One thing to keep in mind is the return traffic. If you don't have similar return path, the traffic may be asymmetrical "

eloborate it litt more please . thanks

New Member

Re: IP Route Question

"One thing to keep in mind is the return traffic. If you don't have similar return path, the traffic may be asymmetrical "

eloborate it litt more please . thanks

Hall of Fame Super Bronze

Re: IP Route Question

If you have 2 links and packets leaves via one interface, the expected return traffic should be via that same interface. If the return traffic is via another interface, then it's considered asymmetrical.

You often see this kind of behavior when you load-balance links. You must ensure both side of the links have the needed routes pointing to the correct interfaces.

Can you elaborate in your questions a bit, please. Thanks

__

Edison.

Hall of Fame Super Silver

Re: IP Route Question

To supplement the answer from Edison, assymetric traffic is not a problem in and of itself (and is found with some frequency where multiple paths are available). But assymetry is a problem if some device is doing statefull inspection and expects responses to arrive on the same interface on which the original packet was tranmitted (typically a firewall or some device providing firewall services). It can also be an issue if you are doing an RPF (Reverse Path Forwarding) check on incoming traffic.

HTH

Rick

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