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IPv6 Security Lab - Routing Protocol Security
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OSPF neighbour authentication
-----------------------------


### Configuring Neighbour Security for OSPFv2 (for IPv4)

Network operators consider it more and more important to turn on neighbour authentication inside their networks as attacks on infrastructure increase and operators seek to use all available tools to secure their networks.

OSPF supports neighbour authentication. This is quite important inside discrete networks to prevent the introduction of improperly configured or unintended equipment.

Each router team will turn on authentication for OSPFv2. This first step will enable the area to support authentication using the *area N authentication message-digest* command. As soon as this is done, all adjacencies will be expected to use neighbour authentication.

An example configuration might be:

  router ospf 10X
   area 0 authentication message-digest


Note that this does not affect the actual adjacencies on the routers – it only tells the router that the area mentioned will use authentication, if it is configured.

### Intra Area Authentication - Part 2

Now that support for authentication in each area has been configured, the second step is to actually set the authentication password to be used, and the interface it has to be used on. The password that should be used for all areas in this example is *cisco*. MD5 encryption should be used rather than the standard simple encryption – to do this, use the *message-digest-key* sub-interface command.

An example configuration for the Core Router might be:


  interface fastethernet 0/0
   ip ospf message-digest-key 1 md5 cisco
  !
  interface gigabit 1/0
   ip ospf message-digest-key 1 md5 cisco
  !
  interface gigabit 2/0
   ip ospf message-digest-key 1 md5 cisco


Notice now that the OSPF adjacencies do not come up unless the neighbouring router has also entered the same configuration and key. Notice also how the OSPF adjacencies were reset as the configuration was entered – security is being introduced, so the adjacencies are reset.

**Note:** the *message-digest-key* allows up to 255 keys to be set per interface. It is generally not recommended to set more than one per interface, as the router will try and communicate with its neighbours using all keys. If a key needs to be upgraded, common practice then is to set a second key, allowing a graceful changeover without compromising the functioning of the network. Once all the routers on the network are using the new key, the old one should be removed.

### Check OSPFv2 operation

Use the various “*show ip ospf*” commands to see the OSPF status of the lab network now. Check the routing and the routing table. If you are missing any adjacencies, work with your neighbouring routers in your AS to work out why, and what might have gone wrong with the neighbour authentication.

### Configuring Neighbour Security for OSPFv3 (for IPv6)

Neighbour authentication for OSPFv3 is no longer built in as it is for OSPFv2, but relies on the IPSEC authentication header support built into IPv6.

Each team will turn on authentication for area 0 using the *area N authentication* command. An example configuration might be:

  ipv6 router ospf 10X
   area 0 authentication ipsec spi 256 md5 0123456789ABCDEF0123456789ABCDEF
  !


Notice now that the OSPFv3 adjacencies do not come up unless the neighbouring router has also entered the same configuration and key. Notice also how the OSPFv3 adjacencies timed out after the configuration was entered – the adjacent router still had not set up OSPFv3 neighbour authentication. Once they also have done this, the adjacency is re-established.

Also, if we want to configure neighbour authentication per area but disable it on a per link basis, we need to use the authentication null option. The following example shows how to disable neighbour authentication on one specific interface, hssi 5/0.

  interface hssi 5/0
   ipv6 ospf authentication null
   ipv6 ospf 1 area 10


### Check OSPFv3 operation

Use the various “*show ipv6 ospf*” commands to see the OSPFv3 status of the lab network now. Check the routing and the routing table. If you are missing any adjacencies, work with your neighbouring routers in your AS to work out why, and what might have gone wrong with the neighbour authentication.

### Aside: Neighbour authentication in IS-IS

This particular lab is not using ISIS as the IGP but the ISIS configuration is included for the sake of completeness. As with most things in ISIS, the neighbour authentication support is much simpler to configure.

While an attack on ISIS is harder as it runs on the link layer alongside IP rather than on top of IP like OSPF, some Network Operators are still prudent and implement neighbour authentication. Notice that for ISIS, the neighbour authentication is applied per neighbour, not per protocol address family, as it would be in OSPF.

The first step for ISIS is to set up the keychain to be used – it has been called “lab-key”. The key “cisco” is used in the example below:


  key chain lab-key
   key 1
    key-string cisco


Once the keychain has been defined, the router interfaces can be individually activated to support authentication. The first step is to enable MD5 for level-2 IS’s:


  interface fastethernet 0/0
   isis authentication mode md5 level-2


And then associate the key-chain we defined earlier with the configured authentication:


  interface fastethernet 0/0
   isis authentication key-chain lab-key level-2


The ISIS adjacencies do not come up unless the neighbouring router has also entered the same configuration and key.

 

BGP neighbour authentication
----------------------------

### Configure passwords on the iBGP sessions

Passwords should now be configured on the iBGP sessions. Go back to the peer-groups which were configured earlier in this workshop and now add passwords to them. For example, here is the peer-group on the Core router:


  router bgp 101
   address-family ipv4
    neighbor ibgp-partial password cisco
    neighbor ibgp-full password cisco
  !
   address-family ipv6
    neighbor ibgp-v6partial password cisco
    neighbor ibgp-v6full password cisco
  !


Do the same for the peer-groups on the border, access and peering routers.

Once the passwords have been added to the IPv4 and IPv6 peer-groups, reset the BGP sessions. Cisco IOS does not automatically reset peerings once passwords have been added to the configuration.

Watch the router logs – with the BGP session neighbour changes being logged, any mismatch in the password should be easy to spot. A missing password on one side of the BGP session will result in the neighbouring router producing these errors:


  %TCP-6-BADAUTH: No MD5 digest from 3.3.3.3:179 to 2.2.2.2:11272
  %TCP-6-BADAUTH: No MD5 digest from 3.3.3.3:179 to 2.2.2.2:11272
  %TCP-6-BADAUTH: No MD5 digest from 3.3.3.3:179 to 2.2.2.2:11272


whereas a mismatch in the configured passwords will result in these messages:


  %TCP-6-BADAUTH: Invalid MD5 digest from 3.3.3.3:11024 to 2.2.2.2:179
  %TCP-6-BADAUTH: Invalid MD5 digest from 3.3.3.3:11024 to 2.2.2.2:179
  %TCP-6-BADAUTH: Invalid MD5 digest from 3.3.3.3:11024 to 2.2.2.2:179


### Configure password on the eBGP session

Passwords should now be configured on the eBGP sessions between your and your upstream. Just use “cisco” as the password on the eBGP session. Here is an example for AS101.

  router bgp 101
   address-family ipv4
    neighbor 100.121.1.1 password cisco
  !
   address-family ipv6
    neighbor 2001:18:0:10:: password cisco
  !


 

Bogon Filtering
---------------

### Configuring Inbound IPv4 BGP Prefix Filtering

Prefix lists allow a network administrator to permit or deny specific prefixes that are sent or received via BGP. Prefix lists should be used where possible to ensure network traffic is sent over the intended paths. Prefix lists should be applied to each eBGP peer in both the inbound and outbound directions.

Configured prefix lists limit the prefixes that are sent or received to those specifically permitted by the routing policy of a network. If this is not feasible due to the large number of prefixes received, a prefix list should be configured to specifically block known bad prefixes. These known bad prefixes include unallocated IP address space and networks that are reserved for internal or testing purposes by RFC 6890/BCP153. Outbound prefix lists should be configured to specifically permit only the prefixes that an organization intends to advertise.

This configuration example uses prefix lists to ensure that no bogon routes are learned or advertised. Create the IPv4 prefix filter named ‘bogon-filter’ (we will do the same for IPv6 shortly):


  ip prefix-list bogon-filter description == IPv4 Bogons ==
  ! Allow our workshop prefixes
  ip prefix-list bogon-filter permit 100.68.10.0/24
  ip prefix-list bogon-filter permit 100.68.20.0/24
  ip prefix-list bogon-filter permit 100.68.30.0/24
  ip prefix-list bogon-filter permit 100.68.40.0/24
  ip prefix-list bogon-filter permit 100.68.50.0/24
  ip prefix-list bogon-filter permit 100.68.60.0/24
  ip prefix-list bogon-filter permit 100.121.0.0/16
  ip prefix-list bogon-filter permit 100.122.0.0/16
  ! All default route so we can propagate in IGP
  ip prefix-list bogon-filter permit 0.0.0.0/0
  ! Drop all the Bogons
  ip prefix-list bogon-filter deny 0.0.0.0/8 le 32
  ip prefix-list bogon-filter deny 10.0.0.0/8 le 32
  ip prefix-list bogon-filter deny 100.64.0.0/10 le 32
  ip prefix-list bogon-filter deny 127.0.0.0/8 le 32
  ip prefix-list bogon-filter deny 169.254.0.0/16 le 32
  ip prefix-list bogon-filter deny 172.16.0.0/12 le 32
  ip prefix-list bogon-filter deny 192.0.0.0/24 le 32
  ip prefix-list bogon-filter deny 192.0.2.0/24 le 32
  ip prefix-list bogon-filter deny 192.168.0.0/16 le 32
  ip prefix-list bogon-filter deny 198.18.0.0/15 le 32
  ip prefix-list bogon-filter deny 198.51.100.0/24 le 32
  ip prefix-list bogon-filter deny 203.0.113.0/24 le 32
  ip prefix-list bogon-filter deny 224.0.0.0/3 le 32
  ip prefix-list bogon-filter deny 0.0.0.0/0 ge 25
  ! Allow everything else
  ip prefix-list bogon-filter permit 0.0.0.0/0 le 32


Note the last line – it has a permit statement, allowing the remaining addresses in the BGP session. Cisco IOS has a default deny for its prefix-list filter. Also remember that we need to allow the address space used in our workshop here too – those are the first 4 permit lines of the prefix-list.

### Apply the prefix-filter to the IPv4 eBGP sessions

We now apply this prefix filter incoming to our external BGP sessions. For example for AS101:


  router bgp 101
   address-family ipv4
    neighbor 100.121.1.1 prefix-list bogon-filter in
  !


Once you have entered the above configuration, refresh the BGP session by entering the following command (example again for AS101). This refresh command applies the newly added BGP configuration to the BGP session.


  clear ip bgp 121 in


### Configuring Outbound IPv4 BGP Prefix Filtering

Note that it is also important to create an outbound prefix lists to announce only the aggregate allocated prefix outbound to the upstream Network Operator. The configuration would look something like the following:


  ip prefix-list upstream permit 100.68.10.0/24
  !
  router bgp 101
   address-family ipv4
    neighbor 100.121.1.1 prefix-list upstream out
  !


Again remember to refresh the BGP session outbound.


  clear ip bgp 121 out


### Configuring Inbound IPv6 BGP Prefix Filtering

Each Group should now repeat the previous steps above using IPv6 instead. First of all, we will create the IPv6 bogon prefix-list:


  ipv6 prefix-list v6bogon-filter description == IPv6 Bogons ==
  ! Allow our workshop prefixes
  ipv6 prefix-list v6bogon-filter permit 2001:db8:10::/48
  ipv6 prefix-list v6bogon-filter permit 2001:db8:20::/48
  ipv6 prefix-list v6bogon-filter permit 2001:db8:30::/48
  ipv6 prefix-list v6bogon-filter permit 2001:db8:40::/48
  ipv6 prefix-list v6bogon-filter permit 2001:db8:50::/48
  ipv6 prefix-list v6bogon-filter permit 2001:db8:60::/48
  ipv6 prefix-list v6bogon-filter permit 2001:18::/32
  ipv6 prefix-list v6bogon-filter permit 2001:19::/32
  ! Allow default route so we can propagate in IGP
  ipv6 prefix-list v6bogon-filter permit ::/0
  ! Drop all the Bogons
  ipv6 prefix-list v6bogon-filter permit 64:ff9b::/96
  ipv6 prefix-list v6bogon-filter permit 2001::/32
  ipv6 prefix-list v6bogon-filter deny 2001::/23 le 128
  ipv6 prefix-list v6bogon-filter deny 2001:2::/48 le 128
  ipv6 prefix-list v6bogon-filter deny 2001:10::/28 le 128
  ipv6 prefix-list v6bogon-filter deny 2001:db8::/32 le 128
  ipv6 prefix-list v6bogon-filter deny 2002::/16 le 128 
  ipv6 prefix-list v6bogon-filter deny 3ffe::/16 le 128
  ! Allow rest of Global Unicast space
  ipv6 prefix-list v6bogon-filter permit 2000::/3 le 48
  ipv6 prefix-list v6bogon-filter deny ::/0 le 128


Note that the logic here is reversed from the IPv4 filter – basically the only routable IPv6 address space is the 2000::/3 Global Unicast address block, so that is what is permitted through our filters. The exceptions to this last permit line are listed in the previous entries of the prefix filter.

### Apply the prefix-filter to the IPv6 eBGP sessions

We now apply the prefix filter to our IPv6 eBGP session (or sessions) with our neighbours, in the same style as we did for IPv4.


  router bgp 101
   address-family ipv6
    neighbor 2001:18:0:10:: prefix-list v6bogon-filter in
  !


Once you have entered the above configuration, refresh the BGP session by entering the following command (example again for AS101). This refresh command applies the newly added BGP configuration to the BGP session.


  clear bgp ipv6 unicast 121 in


### Configuring Outbound IPv6 BGP Prefix Filtering

Note that it is also important to create an outbound prefix lists to announce only the aggregate allocated prefix outbound to the upstream Network Operator. The configuration would look something like the following:


  ipv6 prefix-list upstreamv6 permit 2001:db8:10::/48
  !
  router bgp 101
   address-family ipv6
    neighbor 2001:18:0:10:: prefix-list upstreamv6 out
  !


Again remember to refresh the BGP session outbound.


  clear bgp ipv6 unicast 121 out


### Summary

We have now applied inbound bogon filters for both IPv4 and IPv6 on the eBGP session on our border routers. And we have configured outbound filters on our eBGP sessions to only allow the address block originated by our AS to get to our transit provider.

**Note:** in cases where the upstream provider only supplies the default route, we would not need to do the bogon filtering, but instead replace it with a filter only allowing the default route inbound.