Tag Archives: lisp

A glimpse into LISP Control-Plane traffic

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In our lab we were able to configure LISP and verify connectivity between our two hosts. One thing I noticed was the loss of the first two ICMP packets. Let’s walk through how LISP functions and examine what was happening behind the scene.

Upon receipt of the first packet, the SITE1 router (acting as an ITR) checked the LISP map cache to see if it already had an RLOC mapping for the destination EID (172.16.30.101):

SITE1#sh ip lisp map-cache
LISP IPv4 Mapping Cache for EID-table default (IID 0), 2 entries

0.0.0.0/0, uptime: 00:10:16, expires: never, via static send map-request
  Negative cache entry, action: send-map-request

This negative cache entry tells the router that it needs to send a map request to see if there’s an RLOC mapping available. The router will send a map request for EID 172.16.30.101/32 to the Map resolver at 192.168.255.3, and drop the initial data packet (ping #1) from our host:

LISP-Map-Reply

The Map Resolver/Map Server checks the namespaces that have registered, and looks for the RLOC address of the ETR that is authoritative for the EID prefix:

MR_MS#sh lisp site name SITE2
Site name: SITE2
Allowed configured locators: any
Allowed EID-prefixes:
  EID-prefix: 172.16.30.0/24
    First registered:     00:31:21
    Routing table tag:    0
    Origin:               Configuration
    Merge active:         No
    Proxy reply:          No
    TTL:                  1d00h
    State:                complete
    Registration errors:
    Authentication failures:   0
    Allowed locators mismatch: 0
    ETR 192.168.100.2, last registered 00:00:50, no proxy-reply, map-notify
                        TTL 1d00h, no merge, hash-function sha1, nonce 0x0524E21F-0x489614BB
                        state complete, no security-capability
                        xTR-ID 0xDC4A8044-0x87093251-0x602669CB-0x5B720F12
                        site-ID unspecified
    Locator        Local  State      Pri/Wgt
    192.168.100.2  yes    up          10/50 

Once the Map Server determines the RLOC for the authoritative ETR, it forwards the Map-Request message.  The ETR receives the forwarded Map-Request, and responds with a Map-Reply:

LISP-Map-Reply

Once the SITE1 router receives the reply, it updates the local cache:

SITE1#sh ip lisp map-cache
LISP IPv4 Mapping Cache for EID-table default (IID 0), 3 entries

0.0.0.0/0, uptime: 00:10:35, expires: never, via static send map-request
  Negative cache entry, action: send-map-request
0.0.0.0/1, uptime: 00:09:25, expires: 00:05:34, via map-reply, forward-native
  Negative cache entry, action: forward-native
172.16.30.0/24, uptime: 00:09:22, expires: 23:50:38, via map-reply, complete
  Locator        Uptime    State      Pri/Wgt
  192.168.100.2  00:09:22  up          10/50

Now that the router has a complete LISP cache, it can encapsulate packets in LISP headers and send them on their way.

LISP-Data-Packet-Header

LISP Data Packet Payload

In this setup, it’s interesting to note that we lost the first two ICMP packets to the control-plane process. The first packet was dropped by the SITE1 router as it went through the Map Request/Map Reply process to build the local cache. The second packet actually made it through to the other host, but the response was dropped by the SITE2 router as it also had to build the local cache. You can see some of that below:

Ping response sequence

Once the caches have been built, subsequent attempts are 100% successful:

[root@SITE1 ~]# ping -c 5 172.16.30.101
PING 172.16.30.101 (172.16.30.101) 56(84) bytes of data.
64 bytes from 172.16.30.101: icmp_seq=1 ttl=255 time=1.62 ms
64 bytes from 172.16.30.101: icmp_seq=2 ttl=255 time=1.41 ms
64 bytes from 172.16.30.101: icmp_seq=3 ttl=255 time=1.36 ms
64 bytes from 172.16.30.101: icmp_seq=4 ttl=255 time=1.48 ms
64 bytes from 172.16.30.101: icmp_seq=5 ttl=255 time=1.33 ms

--- 172.16.30.101 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4000ms
rtt min/avg/max/mdev = 1.338/1.442/1.626/0.114 ms

Conclusion

I think there are a few important items to remember about the LISP forwarding process. These probably seem obvious, but I still want to point them out:

  1. The mapping system is really more of a ‘director’, in that it doesn’t actually know the answers to queries, but knows who to talk to find out.
  2. LISP control-plane always uses the same source and destination ports: UDP/4342
  3. LISP data-plane packets are always destined for UDP/4341, but the source port will change.

Cisco has a website dedicated to LISP and you can find a great deal of information there, including the devices and software versions that support LISP.  I’d highly recommend checking it out:  Cisco LISP

Simple LISP Lab

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We’re going to start with a very simple topology:

LISP-topology

Instead of using one of our standard routing protocols to advertise the host networks between the SITE1 and SITE2 routers, we’ll rely on LISP. OSPF will be used to advertise the loopback on the MS/MR router within the Core network. We’ll start configuring LISP assuming the basic network is ready to go.

First, lets setup LISP the SITE1 router:

router lisp
 locator-set SITE1
 192.168.100.1 priority 10 weight 50
 exit
!
database-mapping 192.168.5.0/24 locator-set SITE1
!
ipv4 itr map-resolver 192.168.255.3
ipv4 itr
ipv4 etr map-server 192.168.255.3 key secretkey
ipv4 etr
!

Now we’ll configure LISP on the SITE2 router:

router lisp
 locator-set SITE2
 192.168.100.2 priority 10 weight 50
 exit
!
database-mapping 172.16.30.0/24 locator-set SITE2
!
ipv4 itr map-resolver 192.168.255.3
ipv4 itr
ipv4 etr map-server 192.168.255.3 key secretkey
ipv4 etr
!

Finally, we’ll configure the Mapping Server and Mapping resolver functionality on the MS/MR router:

router lisp
site SITE1
 authentication-key secretkey
 eid-prefix 192.168.5.0/24
 exit
!
site SITE2
 authentication-key secretkey
 eid-prefix 172.16.30.0/24
 exit
!
ipv4 map-server
ipv4 map-resolver
exit

Once this is configured, our LISP infrastructure should be complete. Let’s check:

SITE1#sh ip lisp
  Instance ID:                      0
  Router-lisp ID:                   0
  Locator table:                    default
  EID table:                        default
  Ingress Tunnel Router (ITR):      enabled
  Egress Tunnel Router (ETR):       enabled
  Proxy-ITR Router (PITR):          disabled
  Proxy-ETR Router (PETR):          disabled
  Map Server (MS):                  disabled
  Map Resolver (MR):                disabled
  Delegated Database Tree (DDT):    disabled
  Map-Request source:               192.168.5.1
  ITR Map-Resolver(s):              192.168.255.3
  ETR Map-Server(s):                192.168.255.3 (00:00:55)
  xTR-ID:                           0x3D4C0900-0x95932BE0-0x2F5AF1F6-0x4C919E94
  ...

And over on SITE2:

SITE2#sh ip lisp
  Instance ID:                      0
  Router-lisp ID:                   0
  Locator table:                    default
  EID table:                        default
  Ingress Tunnel Router (ITR):      enabled
  Egress Tunnel Router (ETR):       enabled
  Proxy-ITR Router (PITR):          disabled
  Proxy-ETR Router (PETR):          disabled
  Map Server (MS):                  disabled
  Map Resolver (MR):                disabled
  Delegated Database Tree (DDT):    disabled
  Map-Request source:               172.16.30.1
  ITR Map-Resolver(s):              192.168.255.3
  ETR Map-Server(s):                192.168.255.3 (00:00:16)
  xTR-ID:                           0xDC4A8044-0x87093251-0x602669CB-0x5B720F12
  ...

On the MS/MR Router, we can see that the ETR’s have registered with the LISP mapping system. Without this, LISP wouldn’t know the EID-to-RLOC mapping for each EID.

OTV-RTR3#sh lisp site
LISP Site Registration Information

Site Name      Last      Up   Who Last             Inst     EID Prefix
               Register       Registered           ID
SITE1          00:00:14  yes  192.168.100.1                 192.168.5.0/24
SITE2          00:00:17  yes  192.168.100.2                 172.16.30.0/24

Now, to show that LISP is working correctly, lets first show that we don’t have a route to the opposite site:

SITE1#sh ip route 172.16.30.101
% Network not in table
SITE1#ping 172.16.30.101
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.30.101, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)

SITE2# sh ip route 192.168.5.101
% Network not in table
SITE2#ping 192.168.5.101
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.5.101, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)

And since we didn’t configure a default route, there isn’t anything to fall back on.

Let’s test by pinging the SITE2 host:

[root@SITE1 ~]# ping 172.16.30.101
PING 172.16.30.101 (172.16.30.101) 56(84) bytes of data.
64 bytes from 172.16.30.101: icmp_seq=3 ttl=255 time=1.26 ms
64 bytes from 172.16.30.101: icmp_seq=4 ttl=255 time=4.57 ms
64 bytes from 172.16.30.101: icmp_seq=5 ttl=255 time=1.31 ms
^C
--- 172.16.30.101 ping statistics ---
5 packets transmitted, 3 received, 40% packet loss, time 4421ms
rtt min/avg/max/mdev = 1.268/1.374/1.466/0.086 ms

Looks good except for the two we lost at the beginning. Let’s try the reverse ping now:

[root@SITE2 ~]# ping 192.168.5.101
PING 192.168.5.101 (192.168.5.101) 56(84) bytes of data.
64 bytes from 192.168.5.101: icmp_seq=1 ttl=255 time=1.49 ms
64 bytes from 192.168.5.101: icmp_seq=2 ttl=255 time=1.31 ms
64 bytes from 192.168.5.101: icmp_seq=3 ttl=255 time=1.26 ms
64 bytes from 192.168.5.101: icmp_seq=4 ttl=255 time=4.57 ms
64 bytes from 192.168.5.101: icmp_seq=5 ttl=255 time=1.31 ms
^C
--- 192.168.5.101 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4001ms
rtt min/avg/max/mdev = 1.178/1.278/1.398/0.090 ms

So we have two way communication across our network, using LISP to locate and reach the opposite site. Next time we’ll dig a little deeper on what’s happening behind the scenes.

Cisco LISP

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With technologies like OTV, we need a method to optimize traffic destined for our mobile virtualized hosts, by tracking the location and updating our underlying routing system. One possible solution is known as LISP.

LISP stands for Locator ID Separation Protocol, and its function is to allow you to separate the location component of an IP address, from the identity portion of the address. Or as the Cisco LISP configuration guide states, LISP “implements the use of two namespaces instead of a single IP address.” What does this mean?

With LISP you are introduced to two new concepts:

  • Endpoint Identifiers (EID)
  • Routing Locators (RLOC)

The endpoint identifier (EID) is the address used to identify a specific host — this is the same as the IP addresses you use today, and it is said to be in the LISP namespace. The Routing Locator (RLOC) is the address of a router that is part of the normal routing domain but is connected to the LISP namespace and the non-LISP namespace. The RLOC is said to be part of the non-LISP namespace.

One significant difference with LISP is that you no longer have to advertise the EID address space into the normal routing domain. Instead, you rely on LISP to provide mappings between EIDs and RLOCs, and you route based on the RLOC address.

I like to think of LISP as a DNS-like system for routing, because an important part of LISP is a mapping system that maintains EID-to-RLOC mappings. Just like you use DNS to query for name-to-IP mappings, a LISP router performs a query against a LISP mapping server to find out the RLOC that should be used to reach the desired EID.

Components of a LISP system

An complete LISP infrastructure will consist of many parts:

  • Ingress Tunnel Routers (ITR)
  • Egress Tunnel Routers (ETR)
  • XTR
  • Map Server (MS)
  • Map Resolver (MR)
  • Proxy Ingress Tunnel Routers (PITR)
  • Proxy Egress Tunnel Routers (PETR)
  • PXTR

ITR

The ingress tunnel router receives unencapsulated IP packets from the EID namespace, and is responsible for performing lookups to identify EID-to-RLOC mappings for destination addresses. If the packet is destined for an EID in another LISP namespace, the ITR will encapsulate each packet with a LISP header and route the packet towards the identified RLOC. If the packet is destined for a non-LISP address, the packet is routed without any LISP modifications.

ETR

The egress tunnel router receives LISP encapsulated packets from the non-LISP portion of the network, removes the LISP header, and delivers the unencapsulated packets to the EID. The ETR is also responsible for keeping the Mapping system up to date with EID mappings and responding to Mapping system requests.

LISP XTR

An XTR is a router that performs both ETR and ITR functions.

Map Server

The map server receives EID registrations from ETRs, and responds to map request messages that are forwarded from map resolvers.

Map Resolver

The map resolver receives encapsulated map request messages from ITRs and forwards them to Map Servers that are authoritative for the EID namespace being queried.

PITR/PETR/PXTR

The Proxy ITR/Proxy ETR allows non-LISP sites to communicate with LISP sites, and vice-a-versa, by performing ITR and ETR functionality. They can be deployed separately, or together. If deployed together the device is referred to as a PXTR.

Conclusion

It took me a little while to wrap my head around the LISP concept, and one big help was working with it in a lab environment.  In the next post, I’ll walk through a lab scenario to demonstrate LISP in action.