Inter VS Intra

The Link State protocol compute the best base on Link Stat Data Base (LSDB).
For OSPF, the Intra > Inter > External,
For ISIS,
1. Level 1 intra-area routes with an internal metric
2. Level 1 external routes with an internal metric
3. Level 2 intra-area routes with an internal metric
4. Level 2 external routes with an internal metric
5. Inter-area routes (Level 1 to Level 2) with an internal metric
6. Inter-area external routes (Level 1 to Level 2) with an internal metric
7. Inter-area routes (Level 2 to Level 1) with an internal metric
8. Inter-area external routes (Level 2 to Level 1) with an internal metric
9. Level 1 external routes with an external metric
10. Level 2 external routes with an external metric
11. Inter-area external routes (Level 1 to Level 2) with an external metric
12. Inter-area external routes (Level 2 to Level 1) with an external metric

If the same prefix in LSDB locate in different Level or Area, the Intra-area always the best even you cahnge the Inter-area AD.

Here is a smiple question for you :

R2,R3 link = Level-2
R2,R1 link = Level-1
R1,R3 link = Level-1
R2 Lo0 = Level-2
R3 Lo0 = Level-2
R1 Lo0 = Level-1

1, R1,R2,R3 in the same area.
2, R1 can't using 0/0 to reach either R2/R3.
3, All router Lo0 must reach each other in best way, you can't have suboptimal routing in your network.

Can you do it ?

Multihop EBGP

The common eBGP is over single link. Sometimes may be multi links using on eBGP peering. R2 update NetA and NetB via eBGP peer to R1. If you always want to put NetA into link 1 and NetB into link2 plus redundancy @R1. If any one link down must not impact the traffic.

The redundancy is the big topic in multihop eBGP. What I mean is if F0/0.12 @R1 is down, the traffic will move to F0/0.112 to R2. This is not so hard in Junos. The Junos software can create one more routing table for certain type traffic by using FBF. But in IOS, it's not easy. So I found aonther way to accomplish this.

I will post the answer later. If you have any idea, Let me know.

CLNS

What is CLNS ? The answer is "Connectionless Network Service" It's different from IP. This is one of the issue for Juniper router. Because Juniper router doesn't support CLNS routing in M/T and static route support in J series. And In cisco IOS router you can run DUAL ISIS at the saem time.

Take a look. From JNCIP book :

"Juniper Networks M-series routers support the IS-IS protocol strictly for use in building IP routing tables. There is no support for the routing of OSI Connectionless Network Service (CLNS) network layer packets."

http://www.juniper.net/techpubs/software/jseries/junos93/jseries-config-guide-advanced/configuring-is-is-for-clns.html

This help you Configuring IS-IS for CLNS.

Morakot hit Taiwan a lot

This is a news I don't want post it on my blog, but this one hit Taiwan a lot. I will record this typhoon for the hero who help the victim.

Aug,08,2009 No one know this typhoon will raining 3 meter high water in 2 days! The worst flooding in decades.

Hope they will be fine.

Cisco official Podcast Series

We are here in 2009 and moving into 2010 next year. There are a lot ways we can learning new stuff. Now cisco new Technology Podcasts let you can learn new stuff from website and you also can download it to you Apple series Ipod, Iphone. Take a look.


http://www.cisco.com/en/US/products/products_technology_podcast_listing.html

Dual OSPF process in IOS

I try yo move some different VPN into different path for reduce link utilization reach 95% and packet lost. In my topology, I add lower links between POPs. For the IGP cost which will not have traffic on it. Another one is the next-hop is the same from the same PE. The IOS open a option for you, "bgp next-hop loopback" under vrf config mode. After I change the next-hop, I move to IGP question. In my idea I wanna try to add another IGP domain against the originate. The new lower link will in the new IGP domain and redistributing into the originate IGP. Both are using OSPF. This call "OSPF Redistribution Among Different OSPF Processes" Ref links:

OSPF Redistribution Among Different OSPF Processes
http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080531fd2.shtml

Suboptimal Routing When Redistributing Between OSPF Processes
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00801069aa.shtml

For simple topology :

R1----Fe----R2

﹨___Seri___／

R1 access R2 via 2 type interface "FastEthernet and Serial" Both R1, R2 create 2 Loopback interface. Each interface inside one OSPF domain. And two Redistribution Points(both R1,R2)

The key point is here:

OSPF does not do any OSPF route selection between processes

(for instance, OSPF metrics and route types are not taken into account,

when deciding the route of which process should be installed into the routing table).

The OSPF route selection rule is that intra-area routes are preferred over inter-area routes,

which are preferred over external routes. However,

this rule should apply to routes learned via the same process. In other words,

there is no preference between external routes from one process compared to internal routes of other process.

The preference rule between a given OSPF process and any other process

After redistribution, R1 will see the Loopback interface from R2 via the ower OSPF PID. The way to fix it is "distance" under router config mode. When dual or multiple OSPF running in the same box it's like different protocol (OSPF vs EIGRP). You have to change the external AD in each IGP domain if redistribution between each other. Or the Suboptimal Routing will in your network.

resolve-vpn in Junos

In the MPLS VPN network, There are different between IOS and Junos. There we are talk about the label in each OS.

In IOS, the label can be allocate from LDP/TDP(IGP), or the BGP (ipv4 or vpnv4). This is very important for Inter-AS or CSC which will swap label at border ASBR. if the label can't match the data plane is lost end to end connection.

In the Junos, It's a little complex where in inet.0 or inet.3. First we remind what's the inet.0 and inet.3. For the inet.0, in the JNCIA ebook it's is the table used to store IPv4 unicast routes(OSPF, RIP. ISIS) For the inet.3 table it contains the egress IP address of a MPLS label switched path (LSP).

In the IOS BGP table, if the next-hop is un-reachable it will not forward to the peer, as the same as ipv4 and vpnv4. How about in the vpnv4, if the next-hop not reach via mpls label ?? Well, the answer is BGP routing is work for you but the data plane isn't work. Because the packet will drop at PE router while there is no label to reach remote PE.

For the Junos, It's more technical then IOS. The rule is "If the next-hop in bgp.l3vpn.0 can reach via inet.3. It will not forward to peer" It's simple if I can't reach the peer via a MPLS label I'll not update the BGP route to perr. No black hole in the path.

So, The resolve-vpn command help you to install BGP route update with the label into the inet.3 table. In the Inter-AS and CSC the bgp update will have a label inside the update. And Junos will put BGP label into inet.3 and the BGP update can send to peer.

That's the resolve-vpnwork for you.