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====== IPv6 Lab - BGP ======

===== Configuring iBGP =====

The next step is to configure iBGP mesh between the four routers in each autonomous system. We’ll use a route-reflector set up to handle this, as this is very common practice today, and full mesh iBGP does not scale, as was covered in the presentations.

We will make the core router the route reflector, as is standard practice. The border router will be a client, the access router will be a client, and the peering router will also be a client. Before setting up the iBGP route reflector, we need to consider the following:

-   border router connects to transit ISP, so can in theory receive the entire global routing table from the upstream (either as a default route, or as every individual announced prefix).

-   peering and access routers connect to customers, private and public peers - the peering router should only hear routes that the peers should be able to receive. A common mistake is for peering routers in service provider backbones to carry the full Internet routing table, resulting in bandwidth hijack, misrouted traffic, and so on. The access router only needs routes local to the AS and the default route - it should never need to carry Internet routes.

==== Configuring Core Router iBGP ====

First we set up the core router. We create two peer groups, one for the standard iBGP mesh, the other for use with the access and peering routers. Here is an example:


  router bgp X0
   bgp deterministic-med
   no bgp default ipv4-unicast
  !
   address-family ipv4
    distance bgp 200 200 200
    neighbor ibgp-partial peer-group
    neighbor ibgp-partial description Local Routes only
    neighbor ibgp-partial remote-as X0
    neighbor ibgp-partial update-source loopback0
    neighbor ibgp-partial next-hop-self
    neighbor ibgp-partial send-community
    neighbor ibgp-partial route-reflector-client
    neighbor ibgp-partial filter-list 10 out
    neighbor ibgp-full peer-group
    neighbor ibgp-full description Local Routes only
    neighbor ibgp-full remote-as X0
    neighbor ibgp-full update-source loopback0
    neighbor ibgp-full next-hop-self
    neighbor ibgp-full send-community
    neighbor ibgp-full route-reflector-client
    neighbor 100.68.X.1 peer-group ibgp-full
    neighbor 100.68.X.1 description iBGP with BX
    neighbor 100.68.X.3 peer-group ibgp-partial
    neighbor 100.68.X.3 description iBGP with PX
    neighbor 100.68.X.4 peer-group ibgp-partial
    neighbor 100.68.X.4 description iBGP with AX
  !
   address-family ipv6
    distance bgp 200 200 200
    neighbor ibgp-partialv6 peer-group
    neighbor ibgp-partialv6 remote-as X0
    neighbor ibgp-partialv6 description Local Routes only  
    neighbor ibgp-partialv6 update-source Loopback0
    neighbor ibgp-partialv6 send-community
    neighbor ibgp-partialv6 route-reflector-client
    neighbor ibgp-partialv6 next-hop-self
    neighbor ibgp-partialv6 filter-list 10 out
    neighbor ibgp-fullv6 peer-group
    neighbor ibgp-fullv6 remote-as X0
    neighbor ibgp-fullv6 description Local Routes only  
    neighbor ibgp-fullv6 update-source Loopback0
    neighbor ibgp-fullv6 send-community
    neighbor ibgp-fullv6 route-reflector-client
    neighbor ibgp-fullv6 next-hop-self
    neighbor 2001:DB8:X::1 peer-group ibgp-fullv6
    neighbor 2001:DB8:X::1 description iBGP with BX 
    neighbor 2001:DB8:X::3 peer-group ibgp-partialv6
    neighbor 2001:DB8:X::3 description iBGP with PX
    neighbor 2001:DB8:X::4 peer-group ibgp-partialv6
    neighbor 2001:DB8:X::4 description iBGP with AX
  !
  ip as-path access-list 10 permit ^$


Notice how we have set up one peer-group called ibgp-partial for use with the access and peering routers - its only difference from the peer-group called ibgp-full is that it has one additional line only permit prefixes originated by the local AS to go to that router. So if the upstream provider sends a default route, or any prefixes from the global BGP table, they will now not make their way to the peering router. While we have used an AS-path filter here, we could also use BGP communities (much more scalable!).

==== Originating Prefixes ====

We will now originate our prefixes into iBGP. We will only do this on the core router (common practice is to originate prefixes on the core routers in a network operator’s backbone, never on the peering or border routers). So, returning to the core router, we now add in network statements to cover our IPv4 and IPv6 address blocks. Here is an example:


  router bgp X0
   address-family ipv4
    network 100.68.X.0 mask 255.255.255.0
   address-family ipv6
    network 2001:DB8:X::/48
  !
  ip route 100.68.X.0 255.255.255.0 Null0
  ipv6 route 2001:DB8:X::/48 Null0


Don’t forget the pull up routes for the aggregate - the network statement in Cisco IOS only tells BGP to put that address block into BGP if the match block is in the global RIB - and the simplest way to install it in the global RIB is to set up a static route pointing to the Null0 interface.

==== Configuring Access and Peering Router iBGP ====

We now turn to the access and peering routers, and will configure iBGP on those as well. We’ll follow the same ideas as we used for the Core router, only the access and peering routers are route reflector clients. Here is a configuration example for either the access or peering routers:

  router bgp X0
   bgp deterministic-med
   no bgp default ipv4-unicast
  !
   address-family ipv4
    distance bgp 200 200 200
    neighbor ibgp-rr peer-group
    neighbor ibgp-rr description iBGP with RR
    neighbor ibgp-rr remote-as X0
    neighbor ibgp-rr update-source loopback0
    neighbor ibgp-rr next-hop-self
    neighbor ibgp-rr send-community
    neighbor 100.68.X.2 peer-group ibgp-rr
    neighbor 100.68.X.2 description iBGP with CX
  !
   address-family ipv6
   < do the same for IPv6 >
  !

Where the example says “do the same for IPv6”, simply take the `route-map` name and create an IPv6 variant - for example “ibgp-rrv6”. You cannot use the same name of route-map for the IPv6 peering.

==== Configuring Border Router iBGP ====

We now turn to the border router, and will configure iBGP on that as well. We’ll follow the same ideas as we used for the Core router, only the Border router is a route reflector client. Here is a configuration example:


  router bgp X0
   bgp deterministic-med
   no bgp default ipv4-unicast
  !
   address-family ipv4
    distance bgp 200 200 200
    neighbor ibgp-rr peer-group
    neighbor ibgp-rr description iBGP with RR
    neighbor ibgp-rr remote-as X0
    neighbor ibgp-rr update-source loopback0
    neighbor ibgp-rr next-hop-self
    neighbor ibgp-rr send-community
    neighbor 100.68.X.2 peer-group ibgp-rr
    neighbor 100.68.X.2 description iBGP with CX
  !
   address-family ipv6
   < do the same for IPv6 >
  !


Notice that the peer-group is identical to the one used on the Peering Router.

===== Improving Routing Security =====

There are a few things we need to tidy up here before we continue with the lab.

==== Peering Router ====

The peering router is just that, a router that peers with other network operators. It does not provide any transit. The peers should only see the routes that you want them to see. We’ve made sure of this by putting in a route filter on the core router so that the peering router can only see locally originated routes. But it is also a good idea to null route the default route, as we will soon be distributing a default route around the AS using IS-IS. So on the peering router we now do:


  ip route 0.0.0.0 0.0.0.0 null0
  ipv6 route ::/0 null0


Now if any of the IXP participants point a default route to the local network, the traffic will simply be dumped in the Null interface of the peering router. Only traffic for specific destinations which available in the routing table on the IXP router will be forwarded to the rest of the network. This is a very important **network security** requirement.

==== Border Router ====

The border router connects to the upstream provider, and therefore gives us access to the whole Internet. The upstream provider will usually send us a default route by eBGP (yet to be set up). Once we hear this default route, how should it be propagated around the autonomous system?

It can be propagated using iBGP, but that tends to be non-optimal, certainly when trying to load balance between two or more transit providers, as the BGP best path is just that. If we distribute the default by the IGP instead, then at least the default route becomes the nearest exit, to the nearest border router. So we will now configure this - for example:


  router isis asX0
   default-information originate
  !
   address-family ipv6
    default-information originate
  !


We now should be ready to proceed with the next part of the lab.

===== Adding a customer route =====

Consult the address plan and now set up customer routes on the Access Router pointing to the Customer Router. We’ll just use one IPv4 and one IPv6 customer per Autonomous System. Take the address assigned for the “End User Space 1”; we will simply point a static route for the customer route to the Null0 interface as we do not have a Customer router in our network (at this point). We’ll use a /26 for IPv4 and a /52 for IPv6 out of the “End User Space 1” assignments.

Here is an example for the Access router.

  ip route 100.68.X.64 255.255.255.192 Null0
  ipv6 route 2001:DB8:X:4000::/52 Null0
  !
  router bgp X0
   address-family ipv4
    network 100.68.X.64 mask 255.255.255.192
   address-family ipv6
    network 2001:DB8:X:4000::/52
  !

Once this has been configured you should then see the customer IPv4 /26 and IPv6 /52 visible in the iBGP for the AS. Check on the Border, Peering and Core routers, and make sure the prefix is visible. Use these commands:

  show ip bgp
  show bgp ipv6 unicast

 

===== Configuring the link to the Transit Provider =====

The next step is to set up eBGP with the Transit Provider. The lab instructors will be running the routers for the two Transit Providers and will have already configured them.

==== Physical Link ====

Follow the guidelines in the [IP Address Plan](address-plan) document to configure the link to the upstream. Make sure that you can ping the upstream’s router using both IPv4 and IPv6 - if it doesn’t work, investigate why.

Here is an example configuration for AS60:


  interface fastethernet 0/0
   description Link to TR2
   ip address 100.122.1.10 255.255.255.252
   ipv6 address 2001:19:0:12::1/127
  !


==== IGP ====

**Do not configure any IGP (IS-IS or OSPF) towards the upstream provider!** They are not part of your autonomous system.

==== External BGP ====

We now configure eBGP with the upstream. Again, the configuration on the two transit routers will have already been completed by the instructors, so once configured, the eBGP session should just come up and work.

Here is a configuration example for AS10:


  router bgp 10
   address-family ipv4
    neighbor 100.121.1.1 remote-as 121
    neighbor 100.121.1.1 description eBGP with TRANSIT 1
  !
   address-family ipv6
    neighbor 2001:18:0:10:: remote-as 121
    neighbor 2001:18:0:10:: description eBGP with TRANSIT 1
  !


Once this has been configured, you should now see routes coming from the upstream provider, and you should be able to see your aggregate being sent to your upstream. The commands to see what you are receiving are:


  show ip bgp neigh 100.121.1.1 routes
  show bgp ipv6 uni neigh 2001:18:0:10:: routes


and to show what you are sending:


  show ip bgp neigh 100.121.1.1 advertised-routes
  show bgp ipv6 uni neigh 2001:18:0:10:: advertised-routes


==== Confirmation ====

Check on the Core and Peering Router what you now see in the BGP table. Are there differences? Can you explain what they are, and why?

What does:


  show ip bgp 0.0.0.0 0.0.0.0
  show ip route 0.0.0.0 0.0.0.0
  show ipv6 route ::/0
  show bgp ipv6 uni ::/0


show you on the core router and on the peering router?

You will notice that the default route is being propagated by BGP throughout the AS.

-   On the core router, it will complain of a **RIB failure** when you look at the BGP table, because OSPF has a default route with a lower protocol distance.

-   On the border router, it will complain of a **RIB failure** when you look at the BGP table, because there is a static default route to the Null interface.

While there is nothing wrong with a **RIB failure**, we can just remove the default from being propagated by the iBGP. To do this, we go back to the eBGP session, look for the default, tag it with the *no-advertise* community, and then the border router will no longer announce the default by iBGP.

Here is a configuration example for AS20:


  ip prefix-list default-route permit 0.0.0.0/0
  !
  route-map tag-default permit 10
   match ip address prefix-list default-route
   set community no-advertise
  !
  route-map tag-default permit 20
  !
  ipv6 prefix-list default-v6route permit ::/0
  !
  route-map tag-v6default permit 10
   match ipv6 address prefix-list default-v6route
   set community no-advertise
  !
  route-map tag-v6default permit 20
  !
  router bgp 20
   address-family ipv4
    neighbor 100.121.1.5 route-map tag-default in
   address-family ipv6
    neighbor 2001:18:0:11:: route-map tag-v6default in
  !


To confirm, has the default route now disappeared from the BGP table on the Core and Peering routers? If not, did you remember to do route-refresh after you applied the above configuration?

==== Testing ====

Once this has been completed, test the connectivity. Can you reach the other groups in the class? You should be able to ping all the IPv4 and IPv6 loopbacks across the whole classroom.

Can you see the Internet too? The lab has IPv4 connectivity to the Internet - check that this works by trying a few pings or trace routes to well known destinations (e.g. to 8.8.8.8).


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