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.

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.

Inver-ARP at WAN interface

There is another different between IOS and Junos, the Inverse-ARP behavier, In the JNCIP book said, The Juniper Network router cannot generate IN-ARP request, but IOS will. So the dynamic mapping is only at IOS.

default route in BGP

I want to send a default route to the BGP neighbor, what would you do in IOS and Junos ?

In IOS
router bgp 10

neighbor 1.2.3.4 default-originate

In Junos
no,
By default Junos will announceBGP only, anything else will using policy-statement to accomplish. so, you need to create a static route in routing-option. and export the 0/0 route to the neighbor.

That's another different between IOS, Junos

IOS vs Junos part 1

There are copule different between IOS, Junos, here are the different in OSPF part,

1, router-id in junos without using route-id cmd, the junos will automate send /32 to every are in OSPF PID.

2, stub, NSSA, both will not send out 0/0 at ABR by default.

3, External route cann't summary inside OSPF conifg in Junos.


More ??