Connecting

Connect to the lab server:

local$ ssh-keygen -R netlab.nanocat.net
local$ ssh [email protected]
Password: (see discord)

Connect to your router:

lab@netlab$ list-devices
lab@netlab$ connect DEVICE

Introduction: About BGP ASNs and PI address space allocations

• Your RIR can allocate you your own:
  • an AS number (ASN)
  • IPv4 Provider-Independent (PI) address space
  • IPv6 Provider-Independent (PI) address space
• These allocations are GLOBAL (Internet-wide).
• There is a limited amount of address space, and a limited number of ASNs.
• Each RIR has its own policies for allocation. For example, https://www.ripe.net/manage-ips-and-asns/as-numbers/request-an-as-number
• If you have your own ASN and PI address space, you can ask your Internet Service Provider (ISP) to run a BGP session with you
• If you do not have your own ASN and PI address space, you can use a private ASN and borrow addresses from your ISP

Our new customers

• The customers in our new topology are divided into two groups:
  • those with their own ASNs and PI addresses
  • those without
• You will help customers with their own ASN and PI set up BGP peering sessions with you
• For customers without their own ASN, you will assign a private one, and carve out some of your own address space for them

Topology

Prefix and AS number allocations: https://docs.google.com/spreadsheets/d/1vxVgJI_LhY3NDGJ3icE-4zphmBxUurEvVFgdjafFBzc/edit?usp=sharing

Open this image

Goal

• Find your customers in the spreadsheet
• Allocate ASNs and address space for customers without their own
• Configure BGP sessions for both of your customers
• Verify that it’s all working

Allocate ASNs and address space

• Open the spreadsheet
• For the customers without their own ASN and PI address space:
  • Allocate an ASN from the 32-bit private ASN range
  • Allocate the next available /31 for the link between you and them
  • Allocate a /26 from your /24
    • Remember that you already allocated the first /26 for your PC!

Configure links

• Configure a /31 on their uplink to you
  • Customer gets the lower of the two addresses
• Configure the /31 on your downlink to them
  • You get the higher of the two addresses

Configure customer loopback interfaces

• Configure a new loopback interface on each customer router
  • loopback10
  • use the first IP address from their allocation
  • use the netmask from their allocation

Configure BGP sessions

• On your router, configure two new BGP sessions
  • one for each customer
  • use their /31 link address as the neighbour address
  • use the correct ASN for their remote-as
• On the customer’s routers, configure BGP sessions
  • use the /31 link address as the neighbour address
  • use your own ASN for their remote-as
  • advertise their network with a network statement

Verify and Troubleshoot

• From your PC (which you will need to configure again):
  • traceroute to your two customers’ loopback10 addresses
  • traceroute to other customers’ loopback10 addresses

BONUS ROUND

• Level 1: Steal someone else’s prefix and route it to yourself
• Level 2: Have your customer steal someone else’s customer’s prefix
• Level 3: Stop your customer from stealing someone else’s customer’s prefix

Appendix: configuration snippets

Configure an IP address

!
interface ethernet2
   no switchport
   ip address x.x.x.x/xx
!

Create a loopback interface

!
interface loopback10
   ip address x.x.x.x/xx
!

Configure a BGP session

!
ip routing
!
router bgp XXXX                       <- your ASN
   neighbor x.x.x.x remote-as YYYY    <- neighbor ASN
   network x.x.x.x/xx                 <- announce this network
!

For a network to be announced by BGP, an exactly matching route needs to exist in the routing table.

For a network to be accepted by BGP, the “BGP next-hop” address must be reachable.

Configure your PC

ip address add 192.168.XX.10/26 dev eth1
ip route delete default
ip route add default via 192.168.XX.1