Redistribute multiple default route on BGP

[NAGISWAREN2]

Helo all,

I have a scenarion. Im just beginner to BGP. We having customer with total 16 sites, 2 HQ and 14 branches. all this sites connected via MPLS which running under BGP. The MPLS cloud managed by our ISP.

2 HQ router which connected to Telco UPE (NTU) is running on BGP which establish BGP session to ISP PE router. all other 14 sites actually running on private broadband which connected to MPLS clound. Basically branch site just having a ADSL modem, once dialer get connected, they can communicate to  all other site. Bothe HQ having separate Internet link to access internet. And all the branches accessing internt via HQ 1 internet link. To achive this, in HQ 1 router i jus add below command under router bgp AS ID

neighbor neighbour ID default-originate

And all the branches able to surf internet without no problem. But here we want once the HQ internet is down, we need all branch internet access is diverted to HQ 2 internet link. I know it can be done manually in HQ 2 router by adding the same command. But is there anyway to do it automatically? What if both site HQ 1 and 2 advertised default route? which link will the branch choose? can I advertise default route with metric?

my request in simple form.

If HQ 1 internet link down: branches and HQ 1 should use HQ 2 internet to online

if HQ 2 internet link down : branches and HQ 2 should use HQ 1 internet to online

Anyway to achive this?

[smitesh kharecha]

Hi,

How are sites conected to HQ (logically).

Is there any protocol running between them ?

Regards,

Smitesh

[NAGISWAREN2]

Hi Smitesh,

The protocol between HQ to branches is running over BGP(if not mistaken), but this managed by ISP. only our HQ1 and HQ2 router running on BGP protocol established bgb neighbour to ISP PE router. all other branches running on default route. As i mentioned b4, all sites running on MPLS network.

[Marwan ALshawi]

Simply add same default-originate command on the HQ site toward the ISP

And use bgp AS prepending to make the default route of hq2 les prefered over hqq1 if both of them up

For example use the below config to prepend to the default route assuming your bgp AS number as 100

Ip prefix-list list1 permit 0.0.0.0/0

Route-map map1 permit 10

Match ip address prefix list list1

Set as prepend 100 100

Route-map map1 permit 30

Router bgp 100

Neighbor route-map map1 out

And below is good guide

http://wiki.nil.com/AS-path_prepending_(technical_details)

Hope this help

If helpful rate

[danabersoch]

Marwanshawi is totally right, you need to advertise a default route from the HQ2 site that is less preffered to the HQ1 site so changing a BGP attribute on the route somehow with a route-map is the best way - you could use MED as well if you wanted.

[NAGISWAREN2]

hi marwanshawi

Thanks for the guideline, anyway need some clarification. should I still need to add-in default-originate command in HQ 2 router? in HQ 1 router no changes needed? Thanks for the help.

[Marwan ALshawi]

Yes that's correct

On hq2 you need to the defual-originate

And AS pretending as described above

Hq1 no changes required

Hope this help

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[NAGISWAREN2]

Hi  marwanshawi,

After I applied the below command in HQ 2 router, HQ1 and All other branches unable to communicate to HQ2 LAN. I login to HQ 1 router, and do "sho ip bgp", the LAN segment of HQ 2 not in the list. Meaning to say, the HQ 2 LAN segment nt been advertised.

Neighbor route-map map1 out

Is that because of " ip prefix-list list1 0.0.0.0/0 " command? Because HQ2 router still need advertised in own LAN segment to the neighbour. And all other branches and HQ 1 have to access server placed in HQ 2 LAN. Anyway to trick the prefix list to still advertise HQ 2 own LAN segment without any interuption?

[Marwan ALshawi]

Did you creat a second sequence in the route map map1 with permit as described in my example above ?

Like

Route-map map1 permit 10

Match ip address prefix list list1

Set as prepend xx xx

Route-map map1 permit 40

HTH

[NAGISWAREN2]

Hi marwanshawi,

Ohh sorry, i missed that command. Anyway does that will solve the problem?

[NAGISWAREN2]

Hi marwanshawi,

That solve the problem. But yet another problem came out. I tried to disconnect HQ 1 internet, to see  if HQ 1 fail over to HQ 2 internet , but it doesnt. In HQ 1 router i have default-originate command in place. If I remove this command from HQ1 router, than HQ 1 able to failover to HQ 2 internet.

During default-originate command in place at HQ 1, i did sho ip bgp, and didnt find any default route entry. If I remove that command, than the default route is in place in HQ 1 router. Any idea why?

[Marwan ALshawi]

That's correct this different issue

If you want to have your your static route to be reliable you need to change the way you advertise it to the network with the use is ip sla

I will post an example to you to configure for this

But before that how this router reach the Internet is it directly connected link or it is via another devise advertised via routing

Ir using a static route

Do you have a next hope ip from the Internet ISP ?

Once you provide this onto I can guide to use different way

HTH

and rate the helpful posts for ur original post

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[NAGISWAREN2]

Both HQ1 And HQ2 router dirrectly connected to Internet. Meaning to say, both MPLS and internet connected to same router each site. My default route at each router is using next hop IP of ISP Router. I did use IP SLA at each router to track the availablity of internet link, but the problem, both site router doesnt receive default route from BGP,  if i put default-originate command in HQ1 router.

[Marwan ALshawi · Accepted solution]

Ok

Based on the info provided, a change to the default route injection required on both HQ sites to make it more relable and aware of the availability of the local Internet

Instead of using the default originate command tou will need to use the below logic

Add ip sla track that monitor the availability of the Internet ispmnext hop using icmp

Add a default staticnroute if not already added that point to the ISP next hop ip with the ip sla track created above

The ip sla track will bring this default route down epinephrine the even of icmp to ISP next hop ip ping failur

In this case if the Internet link is down the default route will disappear from the local routing table

In bgp the advertisement of the default route can be associated with the default route existence in the routing table a d this will lead to make it relable because in the case of the Internet link is down the default route will not be advertised

Config example as below assuming

Bgp AS 100

Internet ISP 100.1.1.1

Ip sla monitor 1

icmp-echo 100.1.1.1

timeout 500

ip route 0.0.0.0 0.0.0.0 100.1.1.1 track 10

Now advertise this using bgp using network command

Router bgp 100

Network 0.0.0.0

Same concept must be done on both HQ sites after removing the default originate command

also the previously route map created in HQ 2 must be left as it is to achieve the active standby requirement

Hope this help

[NAGISWAREN2]

Hi marwanshawi,

I understand the part until default routing with ip sla tracking. But in router bgp, u have adversited network 0.0.0.0 , and this same command has to be applied at both HQ 1 and HQ 2. But in here, how the branches identifies which path to choose communicate with HQ1 LAN or HQ2 LAN since both router didnt advertised its own LAN segment. Do i can add another network a.b.c.d command under network 0.0.0.0 where a.b.c.d is the router own LAN ?