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Restrictions for IS-IS Instance per VRF feature

Thomas Schmitt
Level 1
Level 1

Hello,

I'm not sure, if I understand some points right from this "IS-IS Support for an IS-IS Instance per VRF for IP" guide and need some help.

Actually I want to deploy this juniper setup with Cisco IOS-XE software, but apparently Cisco doesn't support multiple IS-IS instances within the same VRF, does it?

Nevertheless, I want to understand the restrictions chapter.

The Points are:

  • IS-IS instances running Connectionless Network Services (CLNS) must have the same system ID.

    "clns router isis tag" command description offers an opposite opinion (and my test too). In case they are talking about "ip router isis tag" command, why do they call it "IS-IS running CLNS"? Or do they speak in generall about IS-IS instance, but in do an opportunity exist, to create an IS-IS instance without CLNS?

  • You can configure only one IS-IS instance to run both CLNS and IP.

    or simple, just one IP instance per VRF is allowed. That's why I can't implement juniper topology

  • IS-IS instances within the same VRF must have unique system IDs, although IS-IS instances located in separate VRFs can have the same system ID.

    But only IPv4 does support VRF and previous point allows just one IPv4 instance per VRF. If they count VRF global as a separate VRF, then the first point can't be true

Other points from that table are clear, except this note - do I understand it right, that I can't use IS-IS VRF feature together with LDP for MPLS VPN service? In That case it's huge disadvantage from IS-IS. Or did I get it wrong? Then can, you explain it please in other words?

ThomasSchmitt_0-1668298134263.gif

 

Note

If you are using LDP, you cannot use the route-target command when configuring a VRF. The router will use BGP for Multiprotocol Label Switching (MPLS) labels.


1 Reply 1

Thomas Schmitt
Level 1
Level 1

Nobody understands what does those restrictions mean? But OK, I got the idea of that guide.

but could at least someone explain last note about route target usage within VRF with LDP and is-is as routing protocol?

If you are using LDP, you cannot use the route-target command when configuring a VRF. The router will use BGP for Multiprotocol Label Switching (MPLS) labels.

1. why do we have that restriction?

I think of RT just as an attribute of VPNv4/6 NLRI and don’t remember any use of it in LDP or IS-IS protocols. Do you know any usage?

2. how should I imagine router switching to label distribution via BGP? will router automatically activate BGP? And how want router distribute labels; will router distribute labels for the IPv4 routes as specified in RFC 3107?

i don’t understand what does this note mean at all

 

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