From: Jonathan Hays (jhays@xxxxxxxx)
Date: Sat May 18 2002 - 17:05:40 GMT-3
When two or more equal cost paths are in the routing table, Cisco IOS
will load balance among them - regardless of whether the routes are
static, directly connected, or from a routing protocol.
On a 2500 series router, if fast switching is enabled the load balancing
would be 'per destination' otherwise load balancing is 'per packet.'
Perhaps the output below would help illustrate:
RouterA#debug ip icmp
ICMP packet debugging is on
RouterA#ping 2.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 32/36/48 ms
RouterA#
00:07:23: ICMP: echo reply rcvd, src 2.2.2.2, dst 192.1.1.1
00:07:23: ICMP: echo reply rcvd, src 2.2.2.2, dst 194.1.1.1
00:07:23: ICMP: echo reply rcvd, src 2.2.2.2, dst 192.1.1.1
00:07:24: ICMP: echo reply rcvd, src 2.2.2.2, dst 194.1.1.1
00:07:24: ICMP: echo reply rcvd, src 2.2.2.2, dst 192.1.1.1
RouterA#sh run
Building configuration...
<snip>
ip route 0.0.0.0 0.0.0.0 Serial0
ip route 0.0.0.0 0.0.0.0 Serial1
RouterA#sh ip route
<snip>
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
C 192.1.1.0/24 is directly connected, Serial0
C 194.1.1.0/24 is directly connected, Serial1
S* 0.0.0.0/0 is directly connected, Serial0
is directly connected, Serial1
RouterA#
RouterA#show ip interface
<snip>
Serial0 is up, line protocol is up
<snip>
IP fast switching is enabled
IP fast switching on the same interface is enabled
<snip>
Serial1 is up, line protocol is up
IP fast switching is enabled
IP fast switching on the same interface is enabled
<snip>
RouterA#
Jonathan
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
D. J. Jones
Sent: Wednesday, May 15, 2002 5:41 PM
To: Giveortake@aol.com; ccielab@groupstudy.com
Subject: Re: Two Default Routes which path?
I don't believe the packets will alternate based on sessions. Once the
first route is installed and used, then the router will continue to use
that until the link goes down. Then it will use the route over serial 1.
----- Original Message -----
From: <Giveortake@aol.com>
To: <ccielab@groupstudy.com>
Sent: Monday, May 13, 2002 6:16 PM
Subject: Two Default Routes which path?
> If I have say a 25xx router or any router with two serial interfaces,
> and
I
> put a default route say
>
> ip route 0.0.0.0 0.0.0.0 serial 0
> ip route 0.0.0.0 0.0.0.0 serial 1
>
> What will happen to the packets if there is no route in the table?
Will
> they all go down the first default route? Will the packets alternate
based
> on sessions?
>
> Amazing how many smart people with lots of experience I have asked
> that do not know the answer to this question including myself!
>
> Thanks,
>
> David
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