Need help in making a default route from the ISP to the internet

[Searon]

Dear Cisco Community,

Can someone explain to me how I make a default route from the ISP to the internet? I'm struggling to find good solutions on this particulary subject on google or youtube.

Thanks in advance.

Kind regards,

Searon

[Georg Pauwen]

From which ISP (there are 4 as far as I can see) do you need the default route to the Internet ? Are you running any routing protocols between the 4 routers ?

[Searon]

Hey Georg,

For the other routers I have to choose a routing protocol by choice aswell for all public subnets. I guess ospf is best choice for the other routers or can I do BGP on all of them?

Yes, I need default route to the internet.

Here is the full topology

I am still learning so any advice is welcome :)

[Giuseppe Larosa]

Hello @Searon ,

in your lab the simplest solution could be the following:

on router labelled ISP-2 you configure a default static route

ip route 0.0.0.0 0.0.0.0 193.190.241.2

( under the hyphotesis that internet router has this IP address o193.190.241.2 on the common LAN segment)

then on ISP-2

router bgp <ISP-AS-number>

network 0.0.0.0

This should be enough to have ISP-2 to advertise in iBGP a default route 0.0.0.0/0 to other ISP-x routers, but would require a full mesh of iBGP sessions.

Hope to help

Giuseppe

[Searon]

Yes, I configured s0/0/0 on router internet with 193.190.241.1, so I do this on the internet router ip route 0.0.0.0 0.0.0.0 193.190.241.1? And configure BGP on all other ISP routers?

[Giuseppe Larosa]

Hello @Searon ,

your understanding is correct.

>> I configured s0/0/0 on router internet with 193.190.241.1, so I do this on the internet router ip route 0.0.0.0 0.0.0.0 193.190.241.1? And configure BGP on all other ISP routers? 

However, my suggestion was based on the first network diagram that you have posted I have just seen that you have posted a more complete topology.

Are you going to use eBGP to connect to the right network block and to the left network block ? I mean the Brussels and Paris branch offices .

Hope to help

Giuseppe

[Searon]

Dear Guiseppe,

The mentor gives us full choice of which routing protocols to use for this labo. Just eBGP is pretty new for me so I'm gonna have to work into it.

What you think of this configuration for ISP2?
isp-2(config)#ip route 0.0.0.0 0.0.0.0 193.190.241.1

isp-2(config)#router bgp 200
isp-2(config-router)#network 0.0.0.0
isp-2(config-router)#network 193.190.240.4
isp-2(config-router)#network 193.190.240.0
isp-2(config-router)#neighbor 193.190.240.12 remote-as 300
isp-2(config-router)#neighbor 193.190.239.4 remote-as 300
isp-2(config-router)#neighbor 193.190.240.8 remote-as 400
isp-2(config-router)#neighbor 193.190.239.0 remote-as 100

I really appreciate your help Guiseppe, looking forward to your answer :)

[Giuseppe Larosa]

Hello @Searon ,

to be more realistic all the ISP-x routers should be in the same BGP AS as ISP-2.

You need also an IGP running on all of them like OSPF

on all ISP-x  with x= 1 to 4

router ospf 100

network 193.194.240 0.0.0.255 area 0

router ISP-2

isp-2(config)#router bgp 200
isp-2(config-router)#network 0.0.0.0
isp-2(config-router)#network 193.190.240.4
isp-2(config-router)#network 193.190.240.0
isp-2(config-router)#neighbor 193.190.240.13 remote-as 200
isp-2(config-router)#neighbor 193.190.239.5 remote-as 200
isp-2(config-router)#neighbor 193.190.240.9 remote-as 200
isp-2(config-router)#neighbor 193.190.239.1 remote-as 200

please note that neighbor commands must refer to real host IP addresses and not to the subnet addresses.

you should do the same on all other routers ISP-x.

When using ebGP then ?  in real world it can be used on the serial links to the branch offices Brussels and Paris.

Hope to help

Giuseppe

[Searon]

When I try I get iBGP not supported :/

isp-2(config)#router bgp 200
isp-2(config-router)#network 0.0.0.0
isp-2(config-router)#network 193.190.240.4
isp-2(config-router)#network 193.190.240.0
isp-2(config-router)#neighbor 193.190.240.13 remote-as 200
isp-2(config-router)#
%Packet Tracer does not support internal BGP in this version. Only external neighbors are supported.

[Giuseppe Larosa]

Hello @Searon ,

I didn't know about this limitation of packet tracer.

It looks like you have to go with eBGP assigning a different AS number to each ISP-x router.

Just remember that with eBGP you just need to peer with directly attached neighbors .

eBGP messages have by default TTL=1.

So in your case each ISP-x will have two eBGP sessions with devices directly connected to it.

The suggested OSPF process is not needed anymore.

I apologize for the misleading info I have provided before.

Hope to help

Giuseppe

[Searon]

Thanks for the great tip about neighbours have to be internal adresses, I didn't know until now. :)

So as I understand the ISP2 router would be like this?

isp-2(config)#router bgp 200
isp-2(config-router)#network 0.0.0.0
isp-2(config-router)#network 193.190.240.0
isp-2(config-router)#network 193.190.240.4
isp-2(config-router)#neig
isp-2(config-router)#neighbor 193.190.239.5 remote-as 300
isp-2(config-router)#neighbor 193.190.240.14 remote-as 300
isp-2(config-router)#neighbor 193.190.240.10 remote-as 400
isp-2(config-router)#neighbor 193.190.240.9 remote-as 100
isp-2(config-router)#neighbor 193.190.239.1 remote-as 100

Thanks for your help Guiseppe.

[Giuseppe Larosa]

Hello @Searon ,

you are near but:

with eBGP only each ISP-x router will be in its own BGP AS number.

As I have explained with eBGP scenario each ISP-x router needs to peer in eBGP only with the directly connected neighbors ad not with the device that is not directly connected to them.

So in the caase of ISP-2 router

isp-2(config)#router bgp 200
isp-2(config-router)#network 0.0.0.0
isp-2(config-router)#network 193.190.240.0
isp-2(config-router)#network 193.190.240.4
! only two eBGP sessions with the routers directly connected to ISP-2 serial interfaces inside ISP block
isp-2(config-router)#neighbor 193.190.239.5 remote-as 300

isp-2(config-router)#neighbor 193.190.239.1 remote-as 100

in similar way you will need to configure all other ISP-x devices.

Notice that ISP-2 default route will be propagated via eBGP to all ISP-x even the one that has no direct eBGP session with ISP-2. This is the key point in an pure eBGP scenario.

Hope to help

Giuseppe

[Searon]

Thanks, I think I got it now my mindset about the neighbor function was totally wrong as you mentioned. I thought you had to neighbor the parts that were unreachable by interface.

"As I have explained with eBGP scenario each ISP-x router needs to peer in eBGP only with the directly connected neighbors ad not with the device that is not directly connected to them."

And now I can ping all routers in my isp group and the internet! :)

Only thing I have left to solve is why the ISP-2 is the only one able to connect to the internet and not the other routers

[Giuseppe Larosa · Accepted solution]

Hello @Searon ,

good news!

the " internet " router needs static routes pointing to the networks inside ISP with next-hop ISP-2 serial interface IP address to it.

only in this way the return of ping started on the other ISP-x can be received.

In order for a ping to be successful both the outgoing and the incoming path have to be built/configured

Hope to help

Giuseppe

[Searon]

Yes, this is it!! I can ping from ISP-4 to the internet now :)

I know It's a bit off topic but for the connection between the local routers (brussel, paris) with the ISP would you also use static routes or bgp?