Secure BGP Template v5.0 29 OCT 2007

Secure BGP Template v5.0 29 OCT 2007

Introduction

BGP is the routing protocal that drives the Internet. Proper configuration of BGP is critical, as mistakes in BGP can result in disaster for both local and remote networks. Further, without a few additional steps to increase the security and defense of BGP, it is possible for miscreants to cause havoc with the BGP and, by extension, routing tables.

This document includes a template configuration for BGP. As with all such templates, this one must be modified to fit the specific requirements of the local network(s). It is not wise to simply cut and paste without a thorough understanding of each command. Comments are included with each command. A more thorough understanding of BGP can be obtained from:

o Internet Routing Architectures, by Bassam Halabi, published by Cisco Press.
o BGP4, by John W. Stewart III, published by Addison-Wesley.

As an aside, debugging BGP issues can be difficult without an external view. To see how the rest of the Internet views my prefix announcements, I use the route servers. Simply telnet to these route servers and issue commands such as sh ip bgp NETBLOCK or sh ip route NETBLOCK. Here is a partial list:

route-views.oregon-ix.net

ner-routes.bbnplanet.net

route-server.cerf.net

route-server.ip.att.net

route-server.east.attcanada.com

route-server.west.attcanada.com

route-server.cbbtier3.att.net

route-server.gblx.net

route-server.as5388.net

route-server.savvis.net

route-server.colt.net

route-server.opentransit.net

route-server.gt.ca

public-route-server.is.co.za (South African routes only)

route-server.belwue.de

route-views.on.bb.telus.com

route-views.ab.bb.telus.com

route-server.ip.tiscali.net

route-server.wcg.net

route-server.manilaix.net.ph

route-server.ip.ndsoftware.net

route-server.utah.rep.net

route-server.he.net

zebra.swinog.ch

This great collection of route servers, plus a few more, can be found by querying the following range of DNS RRs:

routeserver[1-15].sentex.ca

For example:

	dig +short routeserver1.sentex.ca
	route-views.oregon-ix.net.
	198.32.162.100

	- or -

	dig +short routeserver7.sentex.ca
	route-server.gt.ca.
	216.18.63.214

Thanks to Mike Tancsa for making this available!

Thomas Kernen maintains an excellent page of route-servers and more here. Thanks, Thomas! :)

It may also be helpful to receive the bgp-stats report, either daily or weekly. This will help you to size your maximum-prefix statements, as well as maintaining accurate bogon filters. You may subscribe to the bgp-stats report by sending a note to bgp-stats-request@lists.apnic.net with the message text of "subscribe".

While I list the bogon ranges on /8 boundaries, you may prefer a greater level of aggregation. For this I recommend consulting my Bogon List. Don't forget to keep any bogon filters current! You can read more about this at the RIPE NCC De-Bogonising New Addresses page, http://www.ris.ripe.net/debogon/.

Barry Greene and Philip Smith, both of Cisco, have recently released a book entitled Cisco ISP Essentials. This is an excellent collection of clue. You can learn more about it at www.ispbook.com.

Barry also keeps a nice collection of Cisco security documents here.

Credits

My thanks to the following folks for providing input and suggestions!

Roy Arends

Larry Bishop

Oded Comay

Piotr Kucharski

Hank Nussbacher

James A. T. Rice

Joshua Sahala

Mike Tancsa

David Wolsefer

As always, the FIRST community.

Assumptions

• IOS 12.0.X or higher.
  
• Understanding of BGP and the Cisco IOS.
  
• This template is used by a non-transit network.
  
• The local ASN is 111, the remote ASNs are 222 and 333.
  
• The local netblock is 1.88.0.0/19.
  
• The router has already been secured. For details on a secure IOS configuration template, please consult my Secure IOS Template.
  
• This template was crafted for a network that would be dual-homed and BGP peered to two Tier One ISPs.
  
• The IP address of the router used in this template is 172.17.70.1.

Questions, Comments, Suggestions

Feedback is both welcome and encouraged! This document is a work-in-progress as changes to the Cisco IOS, BGP, or corrections to this document appear. Please send any questions along to robt@cymru.com.

Template

The actual commands are in BOLD text so that they stand out from the comment blocks.

! Our ASN is 111
router bgp 111
!
! Don't wait for the IGP to catch up.
 no synchronization
!
! Be a little more forgiving of an occasional missed keepalive.
 no bgp fast-external-fallover
!
! Track and punt, via syslog, all interesting observations about our
! neighbors.
 bgp log-neighbor-changes
!
! Announce our netblock(s) in a manner that does not increase CPU
! utilization. Redistributing from an IGP is dangerous as it increases
! the likelihood of flapping and instability. Redistributing static is
! more stable, but requires the CPU to peruse the routing table at a set
! interval to capture any changes. The network statement, combined with
! a null route, is the least expensive (in terms of CPU utilization) and
! most reliable (in terms of stability) option.
 network 1.88.0.0 mask 255.255.224.0
!
! Our first neighbor, 10.10.5.1, is an eBGP peer with the ASN of 333.
 neighbor 10.10.5.1 remote-as 333
!
! Set for soft reconfiguration, thus preventing a complete withdrawal
! of all announced prefixes when clear ip bgp x.x.x.x is typed.
 neighbor 10.10.5.1 soft-reconfiguration inbound
!
! Type in a description for future reference. Not everyone memorizes
! ASNs. :-)
 neighbor 10.10.5.1 description eBGP with ISP333
!
! Set up a password for authentication.
 neighbor 10.10.5.1 password bgpwith333
!
! Hard-set for version 4. Disabled BGP version negotiation, thus
! bringing the peering session on-line more quickly.
 neighbor 10.10.5.1 version 4
!
! Block any inbound announcments that include bogon networks. A prefix
! list is used because it is:
!  1) Easier on the CPU than ACLs, and
!  2) Easier to modify.
! See the actual bogons prefix-list below.
 neighbor 10.10.5.1 prefix-list bogons in
!
! Announce only those networks we specifically list. This also prevents
! the network from becoming a transit provider. An added bit of protection
! and good netizenship. See the announce prefix-list below.
 neighbor 10.10.5.1 prefix-list announce out
!
! Prevent a mistake or mishap by our peer (or someone with whom our peer
! has a peering agreement) from causing router meltdown by filling the
! routing and BGP tables. This is a hard limit. At 75% of this limit,
! the IOS will issue log messages warning that the neighbor is approaching
! the limit. All log messages should be sent to a remote syslog host.
! The warning water mark can be modified by placing a value after the
! maximum prefix value, e.g. maximum-prefix 250000 50. This will set the
! IOS to issue warning messages when the neighbor reaches 50% of the limit.
! Note that this number may need to be adjusted upward in the future to
! account for growth in the Internet routing table.
 neighbor 10.10.5.1 maximum-prefix 250000
!
! Our next neighbor is 10.10.10.1, an eBGP peer with the ASN of 222.
 neighbor 10.10.10.1 remote-as 222
 neighbor 10.10.10.1 soft-reconfiguration inbound
 neighbor 10.10.10.1 description eBGP with ISP222
 neighbor 10.10.10.1 password bgpwith222
 neighbor 10.10.10.1 version 4
 neighbor 10.10.10.1 prefix-list bogons in
 neighbor 10.10.10.1 prefix-list announce out
 neighbor 10.10.10.1 maximum-prefix 250000
!
! This is our iBGP peer, 172.17.70.2.
 neighbor 172.17.70.2 remote-as 111
!
 neighbor 172.17.70.2 soft-reconfiguration inbound
!
! Again, a handy description.
 neighbor 172.17.70.2 description iBGP with our other router
!
 neighbor 172.17.70.2 password bgpwith111
! Use the loopback interface for iBGP announcements. This increases the
! stability of iBGP.
 neighbor 172.17.70.2 update-source Loopback0
 neighbor 172.17.70.2 version 4
 neighbor 172.17.70.2 next-hop-self
 neighbor 172.17.70.2 prefix-list bogons in
 neighbor 172.17.70.2 maximum-prefix 250000
!
! Do not automatically summarize our announcements.
 no auto-summary
! If we have multiple links on the same router to the same AS, we like to
! put them to good use. Load balance, per destination, with maximum-paths.
! The limit is six. For our example, we will assume two equal size pipes
! to the same AS.
 maximum-paths 2
!
! Now add our null route and the loopback/iBGP route. Remember to add
! more specific non-null routes so that the packets travel to their
! intended destination!
ip route 1.88.0.0 255.255.224.0 Null0
ip route 1.88.50.0 255.255.255.0 192.168.50.5
ip route 1.88.55.0 255.255.255.0 192.168.50.8
ip route 1.88.75.128 255.255.255.128 192.168.50.10
ip route 172.17.70.2 255.255.255.255 192.168.50.2
!
! We protect TCP port 179 (BGP port) from miscreants by limiting
! access. Allow our peers to connect and log all other attempts.
! Remember to apply this ACL to the interfaces of the router or
! add it to existing ACLs.
! Please note that ACL 185 would block ALL traffic as written. This
! is designed to focus only on protecting BGP. You MUST modify ACL
! 185 to fit your environment and approved traffic patterns.
access-list 185 permit tcp host 10.10.5.1 host 10.10.5.2 eq 179
access-list 185 permit tcp host 10.10.5.1 eq bgp host 10.10.5.2
access-list 185 permit tcp host 10.10.10.1 host 10.10.10.2 eq 179
access-list 185 permit tcp host 10.10.10.1 eq bgp host 10.10.10.2
access-list 185 permit tcp host 172.17.70.2 host 172.17.70.1 eq 179
access-list 185 permit tcp host 172.17.70.2 eq bgp host 172.17.70.1
access-list 185 deny tcp any any eq 179 log-input
!
! The announce prefix list prevents us from announcing anything beyond
! our aggregated netblock(s).
ip prefix-list announce description Our allowed routing announcements
ip prefix-list announce seq 5 permit 1.88.0.0/19
ip prefix-list announce seq 10 deny 0.0.0.0/0 le 32
!
! The bogons prefix list prevents the acceptance of obviously bogus
! routing updates. This can be modified to fit local requirements.
! While aggregation is possible - certainly desirable - IANA tends
! to allocate netblocks on a /8 boundary. For this reason, I have
! listed the bogons largely as /8 netblocks. This will make changes
! to the bogons prefix-list easier to accomplish and less intrusive.
! I have listed more specific netblocks when documentation, such as
! RFC1918, is more granular.
! Please see the IANA IPv4 netblock assignment document at the
! following URL:
! http://www.iana.org/assignments/ipv4-address-space
ip prefix-list bogons description Bogon networks we won't accept.
ip prefix-list bogons seq 5 deny 0.0.0.0/8 le 32
ip prefix-list bogons seq 10 deny 1.0.0.0/8 le 32
ip prefix-list bogons seq 15 deny 2.0.0.0/8 le 32
ip prefix-list bogons seq 20 deny 5.0.0.0/8 le 32
ip prefix-list bogons seq 30 deny 10.0.0.0/8 le 32
ip prefix-list bogons seq 35 deny 23.0.0.0/8 le 32
ip prefix-list bogons seq 40 deny 27.0.0.0/8 le 32
ip prefix-list bogons seq 45 deny 31.0.0.0/8 le 32
ip prefix-list bogons seq 50 deny 36.0.0.0/8 le 32
ip prefix-list bogons seq 55 deny 37.0.0.0/8 le 32
ip prefix-list bogons seq 60 deny 39.0.0.0/8 le 32
ip prefix-list bogons seq 70 deny 42.0.0.0/8 le 32
ip prefix-list bogons seq 75 deny 46.0.0.0/8 le 32
ip prefix-list bogons seq 80 deny 49.0.0.0/8 le 32
ip prefix-list bogons seq 85 deny 50.0.0.0/8 le 32
ip prefix-list bogons seq 255 deny 100.0.0.0/8 le 32
ip prefix-list bogons seq 260 deny 101.0.0.0/8 le 32
ip prefix-list bogons seq 265 deny 102.0.0.0/8 le 32
ip prefix-list bogons seq 270 deny 103.0.0.0/8 le 32
ip prefix-list bogons seq 275 deny 104.0.0.0/8 le 32
ip prefix-list bogons seq 280 deny 105.0.0.0/8 le 32
ip prefix-list bogons seq 285 deny 106.0.0.0/8 le 32
ip prefix-list bogons seq 290 deny 107.0.0.0/8 le 32
ip prefix-list bogons seq 295 deny 108.0.0.0/8 le 32
ip prefix-list bogons seq 300 deny 109.0.0.0/8 le 32
ip prefix-list bogons seq 305 deny 110.0.0.0/8 le 32
ip prefix-list bogons seq 310 deny 111.0.0.0/8 le 32
ip prefix-list bogons seq 315 deny 112.0.0.0/8 le 32
ip prefix-list bogons seq 320 deny 113.0.0.0/8 le 32
ip prefix-list bogons seq 390 deny 127.0.0.0/8 le 32
ip prefix-list bogons seq 395 deny 169.254.0.0/16 le 32
ip prefix-list bogons seq 400 deny 172.16.0.0/12 le 32
ip prefix-list bogons seq 405 deny 173.0.0.0/8 le 32
ip prefix-list bogons seq 410 deny 174.0.0.0/8 le 32
ip prefix-list bogons seq 415 deny 175.0.0.0/8 le 32
ip prefix-list bogons seq 420 deny 176.0.0.0/8 le 32
ip prefix-list bogons seq 425 deny 177.0.0.0/8 le 32
ip prefix-list bogons seq 430 deny 178.0.0.0/8 le 32
ip prefix-list bogons seq 435 deny 179.0.0.0/8 le 32
ip prefix-list bogons seq 440 deny 180.0.0.0/8 le 32
ip prefix-list bogons seq 445 deny 181.0.0.0/8 le 32
ip prefix-list bogons seq 450 deny 182.0.0.0/8 le 32
ip prefix-list bogons seq 455 deny 183.0.0.0/8 le 32
ip prefix-list bogons seq 460 deny 184.0.0.0/8 le 32
ip prefix-list bogons seq 465 deny 185.0.0.0/8 le 32
ip prefix-list bogons seq 490 deny 192.0.2.0/24 le 32
ip prefix-list bogons seq 500 deny 192.168.0.0/16 le 32
ip prefix-list bogons seq 510 deny 197.0.0.0/8 le 32
ip prefix-list bogons seq 512 deny 198.18.0.0/15 le 32
ip prefix-list bogons seq 515 deny 223.0.0.0/8 le 32
ip prefix-list bogons seq 520 deny 224.0.0.0/3 le 32
! Allow all prefixes up to /27. Your mileage may vary,
! so adjust this to fit your specific requirements.
ip prefix-list bogons seq 525 permit 0.0.0.0/0 le 27
!
! END