Unanswered Question
Jul 15th, 2008
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Please check the attachment!

I have a central central with connectivity over IPLC circuits to two other office locatoins.

Location Y : Has a 5 E1 links to CO & is connected to Location X over 2 6Mbps MAN link. EIGRP is the routing protocol in use.

Location X : It has two routers, 4 E1 links on each router connecting to CO. EIGRP in use.

CO : Has connectivity to other location on MPLS - EIGRP & BGP are in use on this router at CO

Now, we have acquired a new link - POint to point -1DS3 on Router1 in Location X connected to CO. What should be the routing protocol that can be used? I need to have the DS3 link as the primary link & the 8 E1 links to be as backup.

If I configure EIGRP on the link, All the traffic via location Y to CO will traverse like : Location Y -- via MAN links --> Loaction X -- via DS3 --> CO.

I do not want this to happen.

How do I acheive this ?

What would happen if I configure BGP on the DS3 link ? This way, it'll take care of my 1st requirement, i.e, All the traffic would get routed via DS3 & the 8 E1 links will be in use only when the DS3 goes down. Is that right?

Please help!

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Overall Rating: 4 (1 ratings)
deepa.muralidharan Tue, 07/15/2008 - 21:36
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I have a location - Z in picture. This is connected to both location X & location Y via 4Mb MAN link each. The traffic from this location to CO would be via both Location X & location Y. But now, I need the traffic from Location-Z to be diverted to the DS3 link alone with the other path as a backup.

How can I caheive this ?

Marwan ALshawi Wed, 07/16/2008 - 07:27
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the easiest way to achive it by useing BGP with eigrp as follow

make each site with its own eirgrp AS number and BGP number so u gonna have 4 ASs for each eigrp and bgp

the by useing route map with wieght, local prefrence and as prepend u can achive ur requirments easly and smothly (such as prefering a path over others!)and redistribute each eigrp in its bgp site

so it will be as u have diffrent sites each with its IGP and BGP

try it and if u need any more details let me know

rate if helpful

Marwan ALshawi Wed, 07/16/2008 - 18:06
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by the way i have LABed your topology and i got it work

as the following

cntral location with eigrp 1 and bgp 1

location x eigrp 2 bgp 2

location y eigrp 3 bgp 3

location z eigrp 4 bgp 4

and i increased the local prefrence for the route coming from the central location to the location x through the ds3 to make the prefered path

also on location x i added AS prepend to central through E1s connection to make the return traffic and any traffic from central go through ds 3 connection too.

on location z i increased the wieght between z and x connection to make it prefered too

and its working

and if you wondering why i would sugesst BGP

because as i seen in your topology its multiSite network and with BGP u can have more control on your routing path selction with bgp even more than what i ahve done or u want

in addition in case of any future growth whether this will be adding more locations or routers perlocation

with this sugested method you can adapt easly and quickly

good luck

and rate if helpful

deepa.muralidharan Wed, 07/16/2008 - 20:50
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Thanks for the response. I was thinking on the similar lines & was not sure if it would work.

Now, here's my plan for the topology. Please let me know if I am on the right track.

My objective :

1.To route Location -X & Location Z traffic onto DS3.

2.To have the E1 lines as backup to the DS3 link.


Location x - BGP2; EIGRP

Location Y & Location Z will not be on BGP [ as per requirements]

-->I configure CO & Location X as BGP neighbors.

--> Traffic from Z is pointing to Location X [Router-1] & Location y [Router2] now [EIGRP & Access-lists involved]. Configure the route to "Router-1" as the primary path [increase the preference].

---> Configure BGP route map on the Core switch of Location - X [which in turn connects to the router] to point traffic from Location-z subnet to BGP interface.

-->redistribuet EIGRP into BGP.

With this, the trffic from Location - Z will travererse on the DS3 link. In case of a failure on DS3 link, the traffic can always pass through the E1 links from Location x.

In case of any outage on the link connecting the Location - Z & Location - x, traffic can always flow through Location - Y to reach the CO.

Please let me know if this would work.

Marwan ALshawi Wed, 07/16/2008 - 21:02
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no ur topology looks deffrent !

i got confused

please send me ur exact and final tpology

phisical not logical one

and keep in mind that i would suggest you to put each location in saparate eigrp and bgp AS

and with in each as redestribute btween eigrp and bgp

and between locations only EBGP

then if you need with plicies and route maps help send me detald and exact topology

good luck mate

deepa.muralidharan Wed, 07/16/2008 - 21:16
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Check the attachment!

Let me know if you require any clarification.

Requirement : All traffic from Location X & Location z need to traverse the DS3 link. In case of any failure on this link then, they traverse the 8XE1 links.

But, now Location X traffic might also traverse via this DS3 if we configure EIGRP for the link.

Path -1 : Location Y -2Mb Central Office Least Bandwidth along the path : 2 Mb

Path -2 : Locatoin Y - 6Mb link  Location X  44Mb link Central Office Least Bandwidth along the path : 6 Mb

Among the above two path mentioned, Path -1 will be selected as the best path [Best path].

But I am a little confused with this. If I configure BGP & have my DS3 link on this. I can block the details of network on BGP from reaching Location -Y. This way, can I block the traffic from Location - Y to learn routes over this DS3?

Marwan ALshawi Wed, 07/16/2008 - 21:52
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so let me tell what i undertood from ur requerements and tell if right or not

location X and Z go to ur CO over the ds3 link

location y use its direct connection which is 5XE! to the CO

is that what you want ?

and about bgp ; the idea is we wont block because with blocking we cant achive and backup patch blocking easy with all routing protocols but not always helpful in such a case like your

u can in the future maybe block somthing for extra filtring

but now what we have to do

is use what is called bgp attribute to influnce the bgp path selction in both directions

and that why bgp prefered in multisites deployments also with ISPs because it has the best felxiblity and features among other routing protocols

now confirm to me the topology requerment

if my understanding right give time and i will send u list of config commands requred


deepa.muralidharan Wed, 07/16/2008 - 22:04
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location X and Z go to our CO over the ds3 link

location y uses it's direct connection which is 5XE1 to the CO.

8XE1 links to serve as redundancy to the DS3 link at Location X.

Marwan ALshawi Wed, 07/16/2008 - 22:12
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give me a time maybe maximum over the weekend

and i will try to post it sooner i mean the config ( but i will put IPs from my own with fastethernet interfaces )

the important thing the commands and the ideas how they work regardless what physical media u have 1


Marwan ALshawi Thu, 07/17/2008 - 00:43
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one more question

the link from z to x and from z to y is it through mutilayer switch or router

and if switch is it bgp capable ?

deepa.muralidharan Thu, 07/17/2008 - 00:56
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It's like this :

Location - Z - Router Fastethernet port --> Location X - Switch Fastethernet port.

Marwan ALshawi Thu, 07/17/2008 - 00:59
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ok and the routing configurationu do it in location x on the routers connected to the CO only

i mean no routing config on the switches on location x and y

right ?

deepa.muralidharan Thu, 07/17/2008 - 01:05
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Location X, Y, Z & CO all have EIGRP on the LAN & WAN. i.e,

Loaction X : EIGRP for the 8 E1 links to CO & connectivity to Location Z & Location Y over MAN links.

Location Y : EIGRP for 5 E1 links to CO & connectivity to Location Z & Location X over MAN links.

Location Z : EIGRP & distribution list configs to divert traffic to Location X & Y.

Now, we have got to have DS3 on BGP with the EIGRP routes distributes into BGP & vice versa.

Marwan ALshawi Thu, 07/17/2008 - 01:39
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ok, do location Z,X and y share the same IP addressing subnet?

i mean the connection from the switch on location x have one connection to the MAN and this man connect all locations together Y and Z

and vice versa to others

i just want to know that the connectivty between routers and sites

because in ur topology i can clearly see the connectivty between y to co and x co

but not sure about Y,X,Z as i mentioned above

i know i asked u alot but i want to send somthing helpful

i will avoid the wan and man eigrp

no eigrp between sites

as i told bgp between sites (EBGP)

deepa.muralidharan Thu, 07/17/2008 - 01:59
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Location z : One switch & two routers.

Switch providing LAN connectivity & router-1 to Location x core switch & router-2 to location y core switch. EIGRP is the routing protocol.

Location x : one core switch & two routers. Router 1 & 2 have connectivity to CO via 8 E1 links & router 1 has a ds3 connection to CO. Core switch connected to Location Y switch over 6 Mb X 2 links & connected to location z via a 4Mb link.EIGRP in use.

Location Y : One core switch & two routers. core switch connected to location z [4Mb link] & connected to location Y [6Mb X 2].

CO connected as said.

CO is also connected to other locations via MPLS - BGP.

deepa.muralidharan Thu, 07/17/2008 - 02:12
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Subnet details across locations!

Ex : 10.136.x.x --> Location X

10.128.x.x --> Location Y

10.138.x.x --> Location Z

10.5.x.x --> CO

Also, at each location we have separate subnets for data, voice, printer VLANs

EX:For Location X

10.136.1.x-10.136.5.x(> Data

10.136.20.x-10.136.25.x( --> voice

& so on...

Marwan ALshawi Thu, 07/17/2008 - 02:39
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read it carefully and apply, test it and tell

Marwan ALshawi Fri, 07/18/2008 - 22:45
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is it working or not ?

Marwan ALshawi Mon, 07/21/2008 - 23:16
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if its worked

please, rate the helpful post

and good luck

Giuseppe Larosa Wed, 07/16/2008 - 03:27
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Hello Deepa,

you can achieve what you want with EIGRP by manipulating EIGRP metrics on the MAN links between location Y and location Z

take a sh int of interface connecting to MAN and increase the delay (delay is expressed in tens of microseconds)

Do it on both sides location Y / location X and the MAN link will become just a backup link as you desire.

int fas0/0


changing delay is the best way because EIGRP is cumulative on delay while it takes the inverse of the lowest BW on the path

Hope to help


sdoremus33 Sat, 07/19/2008 - 09:05
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I agree with Giuseppe in order to accomplish your task at hand is to manipulate EIGRP metrics


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