Dual MPLS Routers connected to Dual N5K Core

[shawnkmccullough]

I wanted to ask a question about the diagram I have included.  We are bringing up 2 MPLS WAN connections and would like some specifics on the best design.  We are using BGP to the providers.  From there we have big questions.  We can run BGP internal and are licensed to do so on the N5K's.  The N5Ks are currently using HSRP for inside LAN clients as default gateway.  We want to load balance and provide redundant routes using a dynamic approach.  Should we use BGP internal utilizing the connections between the routers?  Should we use HSRP on the routers?  How best to get the routes to the N5K and should we be considering this?

[Marwan ALshawi]

first of all what you trying to achive

is it active/standby redundancy or loadbalncing the traffic over both CE/MPLS links

if you are using HSRP in the N5K do you have L2 switches connected to the N5K ? are they muti-homed each to both N5K ? if the answer is yes then you could use vPC in the N5K to cluster both N5K as one virtual switch from forwarding point of view and have all your uplinks in forwarding state ( enable RSTP as fallback method )

if you want to load balance from the N5K to the MPLS links you need to add additional link from each N5K to the CEs

then use iBGP or IGP such as ospf between the CEs and N5Ks then use equal cost multi pathing for th eloadbalcing ECMP from N5K to the CEs

if you want active standby, you still need to add additional link between the N5K and CEs if you are going to use vPC

use IGP or iBGP from the CE to N5K and use some routing metric to make the prefered path

please be aware that you need to alige the BGP policies with MPLS SP to make sure inbound and outbound is not gonna be asymitrical

hope this help

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[shawnkmccullough]

We do not see any benefit to vpc. We also do not want additional links between N5K and CE routers. We want there to be load balance between the 2 circuits and allow us to specify which traffic has preference to one provider link more than the other. I would like to keep the direct link between routers and think this can be used as the load balance link and in the even an N5K goes down. I would like to get specifics as to how the config will start to look. Ebgp with one provider is AS x and the other provider is AS y. How do I build my bgp out from the N5K? Bgp between the N5K? Bgp between N5K and upstream CE router? Bgp between CE routers? Really not sure where to start.

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[Marwan ALshawi]

ok in this case lets devid it into 2 parts

first part CEs to MPLS SP

here you need to make sure you have the right BGP polcies to make preference of certain routes over the other, inbound and outbound

i am assuming there is at least a remote site with two links to both ISPs where you need to do same concept to make sure the path is aligned end to end

see the below links for some examples and ideas of BGP

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c95bb.shtml

the second part is the LAN side

since you are using two differnt AS numbers you cannnot run iBGP

however what you can do is to use a common IGP routing between the CEs and N5Ks

redistribute the desired route from each CE to the OSPF/IGP and change the route metric/cost when you redistribute the route, to achieve the path preference and selection from the LAN side

for example if network x.x.x.x has to go via CE1 then when you redistribute network x.x.x.x from CE2 to OSPF increase the cost so that the LAN side will see x.x.x.x with less cost over CE1

if you can do a lab test will be better before you put your config in the production network

please note that you can do it BGP end to end however this will require some advanced config and polices of BGP and i do not recommend you to use it if you are not very experienced with BGP

hope this help

[shawnkmccullough]

Want to go BGP end to end. I believe this to be the most elegant solution. It is true that I am not experienced with bgp but there is no time like now to learn. Especially since I have the perfect testing scenario in a non production mode.

Is it easier to ask a provider to change AS numbers? Should I try to get both providers on the same AS? Will this simplify things?

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[Marwan ALshawi]

well using IGP such as OSPF in the LAN side is not a bad solution

this is one of the best practices to use IGP in you the LAN and BGP in the border/edge of the network !

however if you still want to have only BGP i would say if both AS numbers are the same then you can run in the LAN side iBGP and control all the route with BGP polices only

hope this help

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