Hot answers tagged

9

FEC or 'Forwarding equivalence class' identifies identity for packet which will determine path it will take in the network. For pure IPv4 forwarding, with routing-table 10.0.0.0/24 -> 192.0.2.1 you can think that addresses 10.0.0.0 - 10.0.0.255 share that FEC, as they are treated same way, each of them are going to go to 192.0.2.1. In MPLS typically FEC is ...


9

Yes both LSR[12] could advertise given FEC, say 10.0.0.1/32 with label 10 to each other. Then if IGP says to LSR1 10.0.0.1/32 egress interface is towards LSR2, it'll impose (or swap to) label 10 and send towards LSR2. LSR2 then will find egress interface being something else than towards LSR1 and swap label to what ever that direction has advertised, might ...


9

First, I would recommend checking out Cisco's MPLS FAQ For Beginners, or the NANOG Presentation "MPLS for Dummies" by Richard A Steenbergen. They both have some really good information. With that said, let me address your questions one at a time. (I have excerpted them in part below.) 1: After the initial convergence of the network, LSPs now exist ...


8

Short answer, just use Resource ReSerVation Protocol (RSVP). Long answer, you could use multi-topology-routing and have multiple metrics in each interface and force some packets to different topology than another packets. But I would not really venture there. You might want to talk to your account team that you want segment routing implemented: http://...


6

is a unique label generated per Destination prefix in routing Table or is it per Next-hop in the routing table? ...i have seen customer scenarios approaching 1 million routes... But the MPLS doesn't have any common guidelines for label generation ? Is there not a common rule saying a unique label should be generated per Destination-prefix or per nexthop ? ...


4

Directed LDP is not a term that appears in the LDP specification (RFC 5036.) Perhaps you're trying to understand the difference between Basic Discovery which uses LDP Link Hellos and Extended Discovery which uses Targeted Hellos. Targeted LDP is for exchanging messages with a distant, non-adjacent peer. Targeted LDP can allow routers to use LDP-signaled ...


3

Why there is a need for again source MAC and destination MAC addresses? The original source and destination MAC addresses have no meaning while the packet is in the tunnel. My understanding is that it uses MPLS labeling for switching/routing within the core network. Once it moves out from the PE, it will go to its attachment circuit based on the ...


3

The exact practical scenario when labels might run out is debatable. There are some house-keeping issues also which are not directly related to labels running out but contribute to that effect. Label managers today in major vendors (CSCO, JNPR at least) are programmed so that they need continuous block per label application. Of course this could be fixed, ...


3

Part of it comes down to what's supported, you might have PE's running older code that don't support FEC129. FEC128 multihoming was introduced in Junos 7.5 (see here). FEC129 multihoming was introduced in Junos 12.3 (see here). It's not necessarily that a single VPLS domain ONLY signals with BGP and ONLY discovers with LDP, it's the fact that you can ...


3

FEC Elements are addresses or prefixes which, when included in an FEC TLV as part of a Mapping Message, are mapped to the associated label. If you expand the FEC Element 1 section of your packet capture it will most likely display the element 192.0.2.7/32. That's encoded in the FEC TLV in the format documented in RFC5036 §3.4.1 and each element has the ...


3

Which FEC an egress router has to advertise when using Ordered Control? ... is it expected to announce one single FEC for each of those in its MPLS-Domain or to announce one label for each of those destination? RFC3037, page 3: An LSR using independent control mode advertises FEC-label bindings to peers whenever it sees fit, whereas one using ordered ...


3

Depends on what you mean by a destination. In IPv4 world, FEC is actually an IPv4 prefix (or a route in other words). Simply put a router will map each prefix it learns via IGP to a label. RFC 3036 describes FECs as follows: 2.1. FECs It is necessary to precisely specify which packets may be mapped to each LSP. This is done by providing a FEC ...


2

@Radovan. Refernece to your question "Is H-VPLS applicable for every type of VPLS network? (any other than LDP-based VPLS as in RFC 4762)" , I think H-VPLS was a fix to lessen extensive LDP peering that might result when attempting to configure VPLS using LDP for large number of PEs. The main motivation was to decrease LDP peerings required for VPLS LDP by ...


2

Welcome to Network Engineering! LDP is not a routing protocol, so Administrative Distance does not apply. It's not clear from your question, but how the router forwards depends on what kind of packet it is. If the packet is MPLS, the router will use the label stack to determine where to forward. If the packet is unlabeled, it will use the routing table. ...


2

Some implementations set the ATT bit automatically and provide you a command or knob under a configuration stanza to disable it. i.e on Juniper: ignore-attached-bit Ignore the attached bit on IS-IS Level 1 routers. Configuring this statement enables the routing device to ignore the attached bit on incoming Level 1 link-state PDUs. If the attached bit ...


2

VPWS is a point to point L2VPN, using this technology two geographically remote hosts from the same IP subnet are able to communicate as if they were connected to the same switch. This thing is achieved by the transport of Ethernet frames inside an MPLS tunnel. So if to capture the packet as it travels between two LSRs inside the MPLS core you would get ...


2

Does the show mpls lsp in Junos show only static and RSVP LSPs? Or am I missing something here? It's counter intuitive, but you're correct, only RSVP LSPs are shown with show mpls lsp. It's basically tied to the fact that you configure RSVP LSPs under [protocols mpls], whereas with LDP, you don't. Your best options for LDP are show ldp sessions, show ldp ...


1

The VC will go down if the interface (in your case ge-2/1/5 goes down), so run show interfaces ge-2/1/5 and confirm the Last Flapped: time against your log entries.


1

I'm not sure that FEC128 is limited to just manual discovery of PWs. I've always used the FEC128 multi-home method described in the link with BGP auto-discovery and it works just fine - if I understand your question correctly.


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