Protect BGP Sessions with Passwords and GTSM

Now that you know how to configure EBGP sessions let’s see how you can make it harder for someone to mess them up. Two mechanisms are commonly used to protect EBGP sessions (or the control plane/CPU of the router running them):

• Generalized TTL Security Mechanism (GTSM) described in RFC 5082 (more details)
• Cryptographic protection (but not encryption) of underlying TCP sessions with MD5 checksums or TCP Authentication Option described in RFC 5925.

In this lab, you’ll use:

• GTSM on the EBGP session with ISP-1
• MD5 checksum on the EBGP session with ISP-2¹

If you want to practice BGP session protection with TCP-AO, check out the TCP-AO lab¹.

The routers in your lab use the following BGP AS numbers. Each upstream router advertises an IPv4 prefix and the default route.

Node/ASN	Router ID	Advertised prefixes
AS65000
rtr	10.0.0.1	192.168.42.0/24 10.0.0.1/32
AS65100
x1	10.0.0.10	192.168.100.0/24
AS65101
x2	10.0.0.11	192.168.101.0/24

Start the Lab

Assuming you already set up your lab infrastructure:

• Change directory to basic/6-protect
• Execute netlab up (device requirements, other options)
• Log into your device (RTR) with netlab connect rtr and verify that the IP addresses are configured on all its interfaces.

If you’re using netlab, you’ll get a fully configured lab, including BGP prefix origination on RTR and EBGP sessions between RTR and X1/X2. If you’re using some other lab platform, it’s best if you do this lab exercise after the Advertise IPv4 Prefixes to BGP Neighbors one.

Configuration Tasks

The EBGP sessions with X1 and X2 will not be established because X1 and X2 use EBGP session protection. They might be stuck in Connect, OpenSent or OpenConfirm state as illustrated by the following printout produced on Arista cEOS:

rtr>show ip bgp summary
BGP summary information for VRF default
Router identifier 10.0.0.1, local AS number 65000
Neighbor Status Codes: m - Under maintenance
  Description              Neighbor V AS           MsgRcvd   MsgSent  InQ OutQ  Up/Down State   PfxRcd PfxAcc
  x1                       10.1.0.2 4 65100             11        13    0   76 00:00:14 OpenConfirm
  x2                       10.1.0.6 4 65101             10         8    0    0 00:00:12 Connect

To make the lab work:

• Configure TTL protection (GTSM) on the EBGP session with X1
• Configure MD5 TCP checksum on the EBGP session with X2. The password used by X2 is GuessWhat.

Verification

Check the state of the BGP sessions with a command similar to show ip bgp summary. This is a printout taken from Arista EOS:

rtr#show ip bgp summary
BGP summary information for VRF default
Router identifier 10.0.0.1, local AS number 65000
Neighbor Status Codes: m - Under maintenance
  Description              Neighbor V AS           MsgRcvd   MsgSent  InQ OutQ  Up/Down State   PfxRcd PfxAcc
  x1                       10.1.0.2 4 65100             42        63    0    0 00:00:16 Estab   2      2
  x2                       10.1.0.6 4 65101             17        16    0    0 00:00:04 Estab   2      2

Finally, use a command similar to show ip bgp to display the prefixes your router received from its EBGP neighbors.

Reference Information

This lab uses a subset of the 4-router lab topology. The following information might help you if you plan to build custom lab infrastructure:

Device Requirements

• Customer router: use any device supported by the netlab BGP configuration module.
• netlab has to configure default route origination, MD5 password, and GTSM on the external routers. You’ll find the supported devices in the bgp.session platform support table. You must use Cumulus Linux on the external routers if you’re using netlab release 1.6.3 or older.
• Git repository contains external router initial device configurations for Cumulus Linux.

Lab Wiring

This lab uses a subset of the 4-router lab topology:

Origin Device	Origin Port	Destination Device	Destination Port
rtr	Ethernet1	x1	swp1
rtr	Ethernet2	x2	swp1

Lab Addressing

Node/Interface	IPv4 Address	IPv6 Address	Description
rtr	10.0.0.1/32		Loopback
Ethernet1	10.1.0.1/30		rtr -> x1
Ethernet2	10.1.0.5/30		rtr -> x2
x1	192.168.100.1/24		Loopback
swp1	10.1.0.2/30		x1 -> rtr
x2	192.168.101.1/24		Loopback
swp1	10.1.0.6/30		x2 -> rtr