Glenn,
I was under the impression that turning off the route-cache/ on multiple
interfaces that connect to the same ultimate destination would give you
per-packet load balancing because the route, (in this case, the default)
would not be cached and as each packet entered the router, a route-lookup
would occur for each packet If multiple equal-cost routes are present in the
table, they will be used in a round-robin fashion, thereby granting you
per-packet load balancing...
I believe that, CEF, on the other hand, can be configured for per-packet or
per-destination/source pair load balancing... per-destination/source pair
load balancing is turned on by default according to Cisco, but per-packet
load balancing can be configured if required. So I guess it does either...
See:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/switc
h_c/xcprt2/xccef.htm
I have not done any tests to see exactly how efficiently the router manages
the load balancing with CEF, but it is supposed to alleviate a lot of stress
on the CPU... even on smaller routers.
Scott
-----Original Message-----
From: Glenn M. McMahon [mailto:mcmahon@bbn.com]
Sent: Friday, November 19, 1999 1:12 PM
To: Keoseyan, Scott
Cc: 'Scot Donovan Blair'; cisco-nsp@puck.nether.net
Subject: RE: static routing
At 10:12 AM 11/19/1999 -0500, Keoseyan, Scott wrote:
>Actually that "Gateway set to 0.0.0.0" is what you end up with when you
>specify your default gateway as an interface in the IP route statement...
>goofy, but true.
Agreed.
>What you propose will give him per-packet load balancing... but wouldn't it
>just be better to turn on CEF and run multiple default route statements
>pointing down each T1?
I beg to differ. You will only get per-packet load balancing if you turn on
CEF, what you will achieve by turning off high speed switching is
source/destination load *sharing*. The router's interface will not cache a
destination giving the possibility that the other equal cost paths could be
used the next time someone needs to get to that same destination. The
transmission itself will not be broken down on a packet by packet basis.
For instance, say a user wants to go to www.microsoft.com, the router may
choose Serial 1 as the path but it will keep that path for the entire
conversation as opposed to shooting a packet down serial 1, next packet
down serial 2 and so on.
>One question I had about that strategy is... does CEF work when you specify
>interfaces as gateways in your static route statements... or does one need
>to put IP addresses in for it to work correctly... or does it matter at
all?
It doesn't really matter, both work. I prefer to use the interface name as
the next hop (we use it all the time) which is kinda' nice because if for
whatever reason the WAN port needs to be renumbered, the static route will
not care.
-- Glenn
>Scott
>
>-----Original Message-----
>From: Scot Donovan Blair [mailto:sblair@cerf.net]
>Sent: Thursday, November 18, 1999 11:08 PM
>To: cisco-nsp@puck.nether.net
>Cc: cisco-nsp@puck.nether.net
>Subject: Re: static routing
>
>
>Paul,
>
> Equal cost static routes should work fine to balance between your T1's.
>I would note turning route-cache off the interface may be useful as well
>(this is always debatable). Something that looks odd to me is the below
>snipet of your info..
>
>"Gateway of last resort is 0.0.0.0 to network 0.0.0.0"
>
>Without seeing the config I would be just guessing but it appears as if
>maybe you have default-gateway set to 0.0.0.0.. it's a guess. Im not sure
>what your problems are *exactly* but if you are trying to load balance
>between multiple T1's it should be more than OK to have equal costs
>statics to multiple interfaces .
>
>
>-blair
>AT&T CERFnet
>Backbone Engineering and Planning
>
>| PGP Public Key: www.hfh.com/blair/pgp.txt |
>
>On Thu, 18 Nov 1999, Paul Jacobs wrote:
>
>> I have a simple question (I hope).....
>>
>> I now have 3 T-1's in my 3640 Cisco and need to place static routes to
>> different T-1's so all traffic does not go out 1 single T-1..
>>
>> Below is my current ip route statements:
>>
>> ip route 0.0.0.0 0.0.0.0 Serial1/0:1.1
>> ip route 127.0.0.0 255.0.0.0 Null0
>> ip route 0.0.0.0 0.0.0.0 serial 0/0
>>
>>
>> And my 'sh ip route' output:
>>
>> Gateway of last resort is 0.0.0.0 to network 0.0.0.0
>>
>> C 208.239.156.0/24 is directly connected, FastEthernet1/0
>> S 127.0.0.0/8 is directly connected, Null0
>> 63.0.0.0/24 is subnetted, 1 subnets
>> C 63.64.44.0 is directly connected, Ethernet0/1
>> S* 0.0.0.0/0 is directly connected, Serial1/0:1.1
>>
>> I am doing something wrong because if I define my routes via ip route
>> statement(s) and remove the 0.0.0.0 0.0.0.0 ip route traffic gets in but
>> not out??
>>
>> Any help any one can offer is welcome...
>>
>> Paul Jacobs
>> Network admin
>> http://www.netpacq.com
>>
>>
>
>
This archive was generated by hypermail 2b29 : Sun Aug 04 2002 - 04:12:07 EDT