Per Packet LoadBalancing

Unanswered Question
Nov 20th, 2009

Hi Netpro

I am looking for help to understand Per Packet LoadBalancing Vs CEF LoadBalancing.

Do any conditions applies if you use OSPF or EIGRP as Routing Protocol


How to influence Routing Protocol to route specific routes ( Eigrp or OSPF ), is this alternative to Policy Based Routing


Thanks

FO

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rais Fri, 11/20/2009 - 08:53

CEF switcing supports Session based Load-balancing or per-packet load balancing. So the comparision should be made between the later two. CEF can be compared to process switching. Here is a link for CEF.


OSPF and EIGRP are ways to popullate routing-table. Once that information is there, CEF is still used for load-balancing should the routing table contains multiple routes to a single destination.


Thanks.

Mohamed Sobair Fri, 11/20/2009 - 08:58

HI FO,


Cisco Express Forwarding has two loadbalancing method:


1- Per destination load balancing CEF, which is the default.


2- Per packet load balancing CEF.


CEF is a topolgy driven mechanism, with CEF , the router's RIP is copiend into the CEF FIB.


Ok, with per destination loadbalancing is the cisco recommended loadbalncing Scheme as all forwarded packet arrives in order.


However, with Per packet loadbalancing , its not the recommended Scheme as packet might arrive the destination out of order.


coming to the routing protocols like (Eigrp, OSPF),  I didnt get your question here? Could you please elaborate more on whats exactly you are asking with regard to OSPF and Eigrp?



HTH

Mohamed

Jon Marshall Fri, 11/20/2009 - 09:07

freddy.oram wrote:


Hi Netpro

I am looking for help to understand Per Packet LoadBalancing Vs CEF LoadBalancing.

Do any conditions applies if you use OSPF or EIGRP as Routing Protocol


How to influence Routing Protocol to route specific routes ( Eigrp or OSPF ), is this alternative to Policy Based Routing


Thanks

FO


Freddy


You can influence specific routes within the routing protocol in a number of ways eg. offset-list, changing the bandwidth on the interface, changing the delay on the interface etc..


But you are still influencing which route is used to route a packet to it's destination.


PBR is used when you want to use other criteria rather than just the destination to route the traffic eg. the interface the packet was received on, the source IP address of the packet etc.


So influencing the route metrics and PBR are doing 2 separate things.


Jon

freddy.oram Fri, 11/20/2009 - 09:56

Si jon


Thank You, I got the difference now


What is required to loadShare traffic on Two Wan links running eigrp.

Jon Marshall Fri, 11/20/2009 - 12:30

freddy.oram wrote:


Si jon


Thank You, I got the difference now


What is required to loadShare traffic on Two Wan links running eigrp.


Freddy


EIGRP can load-balance over equal or unequal cost paths. However it's definitely "cleaner" if the paths are equal cost. Basically for EIGRP to use both links it needs to see 2 routes to each destination network one via one link and one via the other. So if you do a "sh ip route " and you see 2 entries for the network then EIGRP will automatically use them both.


If the paths are not equal then only one route will be in the routing table. As i say with EIGRP you can still use the other path using the variance command.


Jon

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