iBGP configuration between three nodes

[Dipesh Patel]

Dear experts,

Kindly suggest for the iBGP configuration between two routers and One CORE switch as shown in diagram :

     

1. iBGP between CE Router A to L3 switch

2. iBGP between CE Router B to L3 switch

3. iBGP between CE Router A to CE Router B

Is ok or I should not configure iBGP between Router to Route and break a loop?

In both the case on router should I configure : neighbor X.X.X.X next-hop-self?

is it required to configure : neighbor X.X.X.X next-hop-self on CORE switch?

Regards

[cadet alain]

Hi,

1) next-hop-self must be configured on the edge routers ,not on the core switch.

2) iBGP full mesh is only needed in a transit AS but this is not your case so i think that only iBGP peerings between each edge router and the core switch should be ok.

Regards.

Alain

Don't forget to rate helpful posts.

[Dipesh Patel]

In my case It's not transit AS.

Than also if I will use ant disadvantage of it? any advantage of it?

[rickymao16]

five stars for your helpful post and also for your very good sense of humor: )

[Giuseppe Larosa]

Hello Dipesh,

if your ISPs ISP1 and ISP2 are providing you only default routes there is no advantage on having an iBGP session between the two CE edge routers.

If the upstream providers ISP1 and ISP2 provide some specific routes in addition to the default route it may be wise to configure the iBGP session between the two CE edge routers.

next-hop-self is only needed on CE edge routers towards core switch (and towards the other CE router if that session is used)

Hope to help

Giuseppe

[Dipesh Patel]

Hi,

WAN Links are MPLS not internet. hence iBGP required.

So my confusion is should I configure iBGP between two Routers or not? If I will do any disadvantage?

Regards

[Giuseppe Larosa]

Hello Dipesh,

so you have an MPLS L3 VPN scenario multihomed with two providers

in this case if all the VPN sites are served by both SPs ISP1 and ISP2,  I would NOT interconnect with an iBGP session the two CE routers.

Here the idea is to have two indipendent control planes one via ISP1 and one via ISP2, the choice to what to use for a specific flow is left to the core switch that is the internal node of each VPN site.

But it is not a good idea to have a direct session between CE edge routers as they would propagate routes learned from ISP1 VPN  to ISP2 VPN and viceversa.

Each SP VPN should be left indipendent so that at least one of the two is working even if something happens in the other SP network. 

Hope to help

Giuseppe

[Dipesh Patel]

Dear Giusepee,

The control Plane of the ISP is different. But There are many locations where only one ISP hecne in some case we need to make onr of location as HUB and transit.

Regards

[Joseph W. Doherty]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

Assuming one CE router has a better or only path to a "WAN" network, you normally would run iBGP between them to convey this information.  Whether to include your L3 switch as a CE iBGP peer, depends on multiple factors such as what you distribute to your IGP, whether the two CE's are on the same VLAN or the links between them and the L3 switch are p2p, etc.

Whether to use next-hop-self depends on what interface subnets are within your IGP.  Often CE <> PE links are not within the IGP, so for those, next-hop-self is often used.

[Dipesh Patel]

LAN IP address of both the Routers as well as CORE swtich interfaces connected to Router LAN interfaces are all in same VLAN. There is no L3 interfaces are configured on CORE switches.

CORE switch will combine the Prefixes from both the ISPs.

[Dipesh Patel]

Dear All,

One more suggation required.

If We have two CORE switches instead of One being configured with HSRP for the End Users and in that case is it required to have iBGP between both the CORE switches?

Please suggest.

Regards

[Joseph W. Doherty]

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

That depends also on many of the same factors noted in my prior post.  Depending on how you configure you logical and physical topologies (one significant change is a direct or L2 switch L2 link between your two CEs), you might run no iBGP at all, iBGP between just the CEs or iBGP between CEs and additional interior routers, such as your two core devices in this question.

[Deben Bhattarai]

HI,

If you are simply learning default routes in L3 from CE , i think it not required to have IBGP peeering between L3's, you can configure tracking [ for default route ] to change the priotity values for HSRP.

[Dipesh Patel]

Dear Deb,

We are not learning defaul routes from the Cloud means it't not internet cloud. It's MPLS cloud. Different Prefixes we are learing from both the links. Some of the prefixes are common on both the links which comming from the location where the same two links are there.

HSRP is ther on CORE switches for local vlans and there is use of it for iBGP.

I have configured Route-map configuring LP = 50 for secondary core switch and LP = 100 for Primary core switch. hecne Router will find the local segment primarily from Primary core switch only.

Now confusion is should we do iBGP between two core swtiches? if we will do si there chances to have loop?

Regards

[Dipesh Patel]

Hi,

We have L2 link between Two core switches and Routers to CORE switches with the same network segments.

At present we have done iBGP between ISP1 MPLS CE router 1 to Both CORE switches as well as ISP2 MPLS CE router 2. But not yet between CORE1 to CORE 2 switches.

All the Routers will recieved Prefixex from the remote locations connected with ISP1 and ISP2.

Our Aim is :

1. Both Link should be working in Aotu Failover mode.

2. We can share the load between two links using BGP attribute manipulation.

3. Autofailver of CORE switch means, when my one core switch goes down than network should be up with secondary core switch.(All the VLANS are configured with HSRP on both core switches).

For that is it required to have iBGP between two CORE switches?

Regards