Unanswered Question
Aug 7th, 2008


Please refer the Diagram. I have 3 offices in a Location-X. The offices are interconnected over 10 Mbps MAN links. I need to connect to Location Y from Location-X. We have 5 E1 point-to-ooint links from Location - X, office -1 connecting to Location Y. Also, I have an MPLS link of DS3 capacity from Office-2 connecting to Location - y.

Office1 ROuter :


Office 2 Router :

EIGRP & BGP are configured. EIGRP to provide the internal routes & BGP for external routes.

Office 3 :

EIGRP is the RP

Now, with this kind of configuration, all the traffic will go over the DS3 MPLS link. why ?

What would happen to traffic from Offices 1, 2 & 3 to Location Y?

I have this problem too.
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Marwan ALshawi Thu, 08/07/2008 - 22:37

Now, with this kind of configuration, all the traffic will go over the DS3 MPLS link. why ?

because the route will be learned via eigrp from one side and via ebgp via ds3 EBGP has less AD than eigrp


DS3 will has less metric in path calculation through eigrp

deepa.muralidharan Thu, 08/07/2008 - 22:46

How is the calculation done ?

On the router at Office -2, we have both EIGRP & BGP configured. We know that BGP will be preffered over EIGRP because of a better AD. Now all traffic to loCtaion y from Office 2, goes via teh DS3.

What would happen to traffic from Office - 1 & office -2 . How is it going to recognise this ?

It's true that DS3 will have less metric in path calculation through EIGRP. But, what we consider is BGP. So how does this work ?

Marwan ALshawi Fri, 08/08/2008 - 01:06

can u clearfy ur question ?

lke from where to where

also dose location y communicat with location x via EBGP?

deepa.muralidharan Fri, 08/08/2008 - 01:33

Location X has 3 offices which communiate via EIGRP.

Location X has two exits to reach Location Y.

Via Office-1 via EIGRP & Office 2 via BGP.

Location Y has EIGRP configured on two routers & BGP on the 3rd router for connectivity over MPLS.

How does traffic from various offices reach Location Y?

Via the DS3 link on BGP ?

I have redistributed the EIGRP traffic into BGP with a metric of 1000.

Marwan ALshawi Fri, 08/08/2008 - 02:15

did u redistibuted bgp into eigrp?

at location x also do the following command

show ip bgp

then u gonna see the prefered path with >

u can also track the path with

traceroute [distination ip]

deepa.muralidharan Fri, 08/08/2008 - 02:27

Yes. I have distributed bgp into eigrp.

Because EBGP is having a better AD than EIGRP, won't all the traffic from Office-2 be traversing DS3 link? Also, since I have distributed BGP to EIGRP won't the path be via DS3 be advertised on EIGRP to Office - 1 & Office 3? This way traffic from all the three offices should go via DS3 link. Right ?

Marwan ALshawi Fri, 08/08/2008 - 03:55

office 3 will see the route offic y through external eigrp becuase it is redistributed from bgp to eigrp

and the effiect of bgp will be on location 2

while other communicating between ech other via eigrp

u can effict the path selction on eigrp thorugh changing the delay on the interface configuration level

keep in mind eigrp considr path cost, metric delay in path calculation

Edison Ortiz Fri, 08/08/2008 - 06:23

Now, with this kind of configuration, all the traffic will go over the DS3 MPLS link. why ?

What would happen to traffic from Offices 1, 2 & 3 to Location Y?

With this kind of configuration, you will have asymmetrical routing.

Traffic from Location Y to Location X: Office 3 will prefer the DS3 since they are using eBGP, however the return traffic will go via Location X: Office 1 since it knows about Location Y via EIGRP internal instead of EIGRP External which is the routing path towards Location X: Office 2 (redistribution from BGP to EIGRP takes place there).




Marwan ALshawi Fri, 08/08/2008 - 06:37

hi Edison i got the idea from the beging but didnt complete the vision in my mind

now u helped in completing this vision

i would say u r 5+


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