LISP site is a set of routers in an edge network that are under a single technical administration. LISP routers in the edge network are the demarcation points to separate the edge network from the core network.

An MS implements part of the distributed LISP mapping database by accepting registration requests from its client Egress Tunnel Routers (ETRs) and aggregating the successfully registered EID prefixes of ETRs.

An RLOC is an IPv4 or IPv6 address of an Egress Tunnel Router (ETR).

The traceroute tool is used to discover the routes that packets take when traveling to their destination.

A site is best conceptualized as an authentication domain: A set of ETRs under the same administrative control. The map server authenticates all ETRs in a site using the same shared key. Without the concept of a site, the map server would be required to have prior knowledge of every ETR in the network along with its authentication key. Site managers will not be able to deploy new ETRs without changing the configuration of the map servers. When a site is considered as an authentication domain as opposed to a topological grouping, then it is easy to see that the benefit of site ID qualification resides in the ability of reaching an EID prefix through ETRs under different administrative control.

With Site ID Qualification, the map server can have the same prefix configuration under multiple sites. The name of the feature stems from the requirement that any two sites with at least one prefix in common must be qualified with a unique site IDs.

When TTL propagation is enabled the traceroute tool can display all middle hops between an LISP ITR and ETR. However, when RLOC and EID are of different address-family the traceroute output is undesirable.

When the above cross address-family situation exists, LISP does not propagate TTL between inner and outer IPv4 or IPv6 headers. During encapsulation, ITR uses the maximum permissible TTL in the outer header instead of using the TTL value from the inner header.

It is better to make the LISP tunnel between the ITR and ETR appear as a single hop to the client of traceroute. This is done through the disable-ttl-propagate configuration CLI either for a specific eid-table or the entire router lisp tag.

Note	The TTL propagation is turned on automatically.

site A
    conf t
router lisp 
site A
site-id 1
authentication-key key1
eid-prefix 1.2.0.0/16 accept-more-specifics


site B
   conf t
router lisp 
site A
site-id 1
authentication-key key2
eid-prefix 1.2.0.0/16 accept-more-specifics 

When a site ID registration is received, the map server searches for the longest matching configured prefix. If the resulting prefix is less specific than the registration and does not have "accept-more-specifics" keyword, the registration is rejected; otherwise it is authenticated using the key of the site associated with the prefix. In this example "lazy" map server configuration is used so that an ETR can register any prefix with the map server.

Lazy Map Server Configuration:

Note	Setup a new MSMR that has the same lazy configuration for two different sites.

enable
conf t
router lisp
 locator-table default
 site A
  site-id 100
  authentication-key key1
  eid-prefix 0.0.0.0/0 accept-more-specifics
  eid-prefix 2000:AAAA:BBBB::/96 accept-more-specifics
  exit
 !
 site B
  site-id 200
  authentication-key key2
  eid-prefix 0.0.0.0/0 accept-more-specifics
  eid-prefix 10.0.0.0/8 accept-more-specifics
  eid-prefix 21.0.0.0/8 accept-more-specifics
  eid-prefix 2000:BBBB:AAAA::/96 accept-more-specifics
  exit
 ipv4 map-server
 ipv4 map-resolver
 ipv6 map-server
 ipv6 map-resolver
 exit

enable
configure terminal
router lisp
eid-table default instance-id 0
disable-ttl-propagate
end

enable
configure terminal
router lisp
disable-ttl-propagate
end

Perform this task to verify the TTL Propagate Disable feature which is enabled automatically in the LISP network. In this example, a LISP site uses a single edge router that functions as both ITR and ETR (known as an xTR). Routing Locators (RLOCs) are in IPv4. EID prefixes are in both IPv4 and IPv6. The LISP site registers to two map server/map resolver (MSMR) devices in the network core. The topology used in verifying TTL Propagate Disable is as shown in the figure below.

The components as shown in the topology are described below:

Note	An IPv6 EID and IPv4 RLOC traceroute output will hide the middle hops between ITR and ETR even when TTL propagation is not disabled.

After disabling TTL propagation, an IPv4 EID over IPv4 RLOC traceroute output appears as below on Host A:

Device# traceroute 192.168.0.22

Type escape sequence to abort.
Tracing the route to 192.168.0.22
VRF info: (vrf in name/id, vrf out name/id)
1 203.0.113.11 1 msec 1 msec 0 msec
2 10.40.40.21 1 msec 1 msec 1 msec
3 192.168.0.22 0 msec 2 msec *