Video Blogs

I am quite busy with my studies now that I don't have time to blog. I am thinking of using Camtasia and instead do a Video blog, saves a lot of time and the explanation will be real time. I want to get active in posting again as the visits in this site seems to be increasing.

Let me know if this is a good idea. Thanks!

NAT Stateful Failover

When the word "stateful" is mentioned in the networking world, it usually means that the router or a firewall keeps records of the sessions created. Stateful failover means that whatever sessions that have been recorded in one device the other backup device has a knowledge of it and can act as a backup without those sessions torn down in case the main device fails. It will function as the same as the primary one. NAT has also the failover functionality. This lab will focus on configuring Dynamic NAT failover.

R3 and R4 are NAT routers. R3 is the primary and R4 is the back up NAT router. These must be configured so that 
R4 will provide stateful failover. Subnets in R1 1.1.1.1/32 - 1.1.1.5/32 should be translated to 
123.123.123.1 - .5 /24. The host side ip address must match e.g. 1.1.1.1/32 = 123.123.123.1/32.

These have been preconfigured:
1. OSPF on all routers.
2. Default route and floating static default route in R5.(for 123.123.123.0/24 reachability)
3. Ip OSPF cost in the links from R2 to R3 and R3 to R5 to disable equal cost path load balancing.

1. First let's configure which is the inside and outside part in the NAT configuration.

R3(config)#int se0/2
R3(config-if)#description connected to R2
R3(config-if)#ip nat inside
R3(config-if)#int se0/3
R3(config-if)#description connected to R5
R3(config-if)#ip nat outside

R4(config)#int se0/2
R4(config-if)#description connected to R2
R4(config-if)#ip nat inside
R4(config-if)#int se0/0
R4(config-if)#description connected to R5
R4(config-if)#ip nat outside

2. Configure an access-list list that will match the IP addresses of Loopback0 in R1 and configure a NAT pool where we will get the translations.

Note: The "match-host" keyword makes it possible for exact host to host translation 1.1.1.1/32 = 123.123.123.1/32, .5 = .5 the 
last octet in the ip address will be the same value. It will match the host portion of the IP address.

R3(config)#access-list 1 permit 1.1.1.0 0.0.0.255
R3(config)#ip nat pool LOOPBACK 123.123.123.1 123.123.123.5 prefix-length 24 type match-host

R4(config)#access-list 1 permit 1.1.1.0 0.0.0.255
R4(config)#ip nat pool LOOPBACK 123.123.123.1 123.123.123.5 prefix-length 24 type match-host

3. Configure a NAT stateful ID. This is what makes the stateful failover possible. This configuration will determine which is the primary NAT router and the backup.

R3(config)#ip nat stateful id 1      ----------> This is locally significant.
R3(config-ipnat-snat)#primary 23.23.23.3
R3(config-ipnat-snat-pri)#peer 24.24.24.4
R3(config-ipnat-snat-pri)#mapping-id 1   ---------> This should match on the routers.
R3(config-ipnat-snat-pri)#exit


R4(config)#ip nat stateful id 1        ----------> This is locally significant.
R4(config-ipnat-snat)#backup 24.24.24.4
R4(config-ipnat-snat-pri)#peer 23.23.23.3
R4(config-ipnat-snat-pri)#mapping-id 1  ---------> This should match on the routers.
R4(config-ipnat-snat-pri)#exit

The "peer" keyword here will do that trick on making the 2 routers related. The ip addresses configured on the "primary" and "backup" parameters should be one of the IP addresses in the router which is configured with the "ip nat inside" command. Otherwise, you will get an error message that its not a match.If 2 backups are configured and they are peer with each other, they won't establish a relationship. A router can be configured as a primary for one mapping-id and back up for another.

After configuring these commands, let's see the logs created by the routers.

R3#
*Mar  1 01:36:33.783: %SNAT-5-PROCESS: Id 1, System start converging
*Mar  1 01:36:45.871: SNAT (Receive): CONVERGENCE Message for Router-Id: 1 from Peer Router-Id: 1's entries
*Mar  1 01:36:45.871: %SNAT-5-PROCESS: Id 1, System fully converged

R4#
*Mar  1 01:34:11.803: %SNAT-5-PROCESS: Id 1, System start converging
*Mar  1 01:34:11.811: %SNAT-5-PROCESS: Id 1, System fully converged
*Mar  1 01:34:48.767: %SNAT-5-PROCESS: Id 1, System start converging
*Mar  1 01:34:50.791: SNAT (Receive): CONVERGENCE Message for Router-Id: 1 from Peer Router-Id: 1's entries
*Mar  1 01:34:50.795: %SNAT-5-PROCESS: Id 1, System fully converged

Let's do a show command that will check the status of the Stateful Failover NAT.

R3#show ip snat distributed

Stateful NAT Connected Peers

SNAT: Mode PRIMARY
  : State READY
  : Local Address 23.23.23.3
  : Local NAT id 1
  : Peer Address 24.24.24.4
  : Peer NAT id 1
  : Mapping List 1

R4#show ip snat distributed

Stateful NAT Connected Peers

SNAT: Mode BACKUP
  : State READY
  : Local Address 24.24.24.4
  : Local NAT id 1
  : Peer Address 23.23.23.3
  : Peer NAT id 1
  : Mapping List 1

4. Configure the IP NAT translation statement mapping access-list 1 and the NAT pool created.

R3(config)#ip nat inside source list 1 pool LOOPBACK mapping-id 1

R4(config)#ip nat inside source list 1 pool LOOPBACK mapping-id 1

5. Now let's test NATing by pingin 5.5.5.5 sourcing from the IP's on Loopback0 on R1. (Will not be shown) We can do "debug ip nat" on R3 and R4, but will only see output in R3 since the traffic passes there. For the sake of a shorter post I will not display the output.

6. Let's check the translation on R3, our main NAT router and afterwards check if R4 is getting the information from the NATing table.

R3#sh ip nat tran
Pro Inside global      Inside local       Outside local      Outside global
icmp 123.123.123.1:20  1.1.1.1:20         5.5.5.5:20         5.5.5.5:20
--- 123.123.123.1      1.1.1.1            ---                ---
icmp 123.123.123.2:19  1.1.1.2:19         5.5.5.5:19         5.5.5.5:19
--- 123.123.123.2      1.1.1.2            ---                ---
icmp 123.123.123.3:18  1.1.1.3:18         5.5.5.5:18         5.5.5.5:18
--- 123.123.123.3      1.1.1.3            ---                ---
icmp 123.123.123.4:17  1.1.1.4:17         5.5.5.5:17         5.5.5.5:17
--- 123.123.123.4      1.1.1.4            ---                ---
icmp 123.123.123.5:16  1.1.1.5:16         5.5.5.5:16         5.5.5.5:16
--- 123.123.123.5      1.1.1.5            ---                ---

R4#sh ip nat tran
Pro Inside global      Inside local       Outside local      Outside global
icmp 123.123.123.1:20  1.1.1.1:20         5.5.5.5:20         5.5.5.5:20
--- 123.123.123.1      1.1.1.1            ---                ---
icmp 123.123.123.2:19  1.1.1.2:19         5.5.5.5:19         5.5.5.5:19
--- 123.123.123.2      1.1.1.2            ---                ---
icmp 123.123.123.3:18  1.1.1.3:18         5.5.5.5:18         5.5.5.5:18
--- 123.123.123.3      1.1.1.3            ---                ---
icmp 123.123.123.4:17  1.1.1.4:17         5.5.5.5:17         5.5.5.5:17
--- 123.123.123.4      1.1.1.4            ---                ---
icmp 123.123.123.5:16  1.1.1.5:16         5.5.5.5:16         5.5.5.5:16
--- 123.123.123.5      1.1.1.5            ---                ---

Though the traffic did not pass through R4, it knows the translation. Notice that the host part of the original ip address and the translated ip address is the same. This is the result of the "match=host" keyword.
Let's see if the failover information by R3 is passed to R4 by a show command.

R4#sh ip snat peer 23.23.23.3

Show NAT Entries created by peer: 23.23.23.3

Pro Inside global      Inside local       Outside local      Outside global
--- 123.123.123.1      1.1.1.1            ---                ---
--- 123.123.123.2      1.1.1.2            ---                ---
--- 123.123.123.3      1.1.1.3            ---                ---
--- 123.123.123.4      1.1.1.4            ---                ---
--- 123.123.123.5      1.1.1.5            ---                ---
icmp 123.123.123.5:16  1.1.1.5:16         5.5.5.5:16         5.5.5.5:16
icmp 123.123.123.4:17  1.1.1.4:17         5.5.5.5:17         5.5.5.5:17
icmp 123.123.123.3:18  1.1.1.3:18         5.5.5.5:18         5.5.5.5:18
icmp 123.123.123.2:19  1.1.1.2:19         5.5.5.5:19         5.5.5.5:19
icmp 123.123.123.1:20  1.1.1.1:20         5.5.5.5:20         5.5.5.5:20

In the even that R3 and the traffic goes to R4, the sessions need not to be restarted as there are already existing translations on R4 which have been passed by R3. Let's shut down the interface in R3 and lets show how R4 reacts.

R4#
*Mar  1 02:11:15.819: %SNAT-5-ALERT: BACKUP staging recovery, replacing Primary
*Mar  1 02:11:15.819: %SNAT-5-PROCESS: Id 1, System start converging
*Mar  1 02:11:15.827: %SNAT-5-PROCESS: Id 1, System fully converged

It places itself as the primary NAT router but the translations that its learned from R3 will continue to be in place. Once R3 goes back up, it will put itself again the backup NAT router.

CCIE Written Cleared

Finally, I have cleared the written exam last week. This doesn't mean I will stop with the theory stuff, in fact I am reading again the certification guide and some QoS books. I am currently doing Narbik Kocharian's Labs Workbook "The Gap from CCNP to CCIE". Though this might be considered an old workbook by some, but the topics here still apply to the current blueprint. I don't have my own rack so I basically do the labs that can be done in GNS3. I am skipping some topics that can only be done in 3550/3650 switches which I will do in a free community lab that I know of. I am halfway through the topics after this I will do the latest Kocharian's workbook. I might as well consider purchasing Kocharian's troubleshooting labs as I find the sample lab very amusing.

I am not promoting Micronics Training in any way. I really like Narbik's approach: Study the technology one at a time and do as much exploration on one topic. This kind of approach IMHO can really make the candidate understand the topic thoroughly. Many candidates fall into the mistake of doing right away the mock labs like crazy but never really explored the topic one after another. Understanding (again IMHO) what you are configuring is a key to passing the lab.

I have not enrolled in any bootcamp but would love to. My primary reason is MONEY, I don't have tons of it. I am a self paying CCIE candidate. Since I can't attend a bootcamp, I read books and visit Cisco Univercd. We have a saying back home and I paraphrase, "If you can't buy a longer blanket, better learn to fit yourself into the blanket", and this is exactly what I am doing.

My plans for doing the lab will be on January 2011, probably take it in Hong Kong. If I feel that I am ready before that, might consider the mobile lab in Singapore by November. I am spending at least 3 hours a night, and a few hours in the office (if not busy) studying and doing some labs on GNS3. For the next 8 months, I will have little to no social life (I never had one before anyways :D). Good day mates and hold on to the Cisco Dream!

No Updates, Yet!!!

I have no time to write a technical blog as of now as I am currently in transition moving from my current company to a new one. I have to do all the necessary stuff needed for this move. Currently I am reading CCIE Routing and Switching Exam Certification Guide, 4th Edition as preparation for my CCIE written mid this year. I don't have much lab time yet but I do have time reading the concepts I have studied when I took my CCNP. My target is Written this year and probably late this year or early to mid next year for my lab attempt. Will be posting something technical here probably 2 weeks from now.