{"id":635,"date":"2018-10-26T22:52:29","date_gmt":"2018-10-26T22:52:29","guid":{"rendered":"http:\/\/feralpacket.org\/?p=635"},"modified":"2018-10-26T22:52:29","modified_gmt":"2018-10-26T22:52:29","slug":"multi-protocol-label-switching-mpls-notes","status":"publish","type":"post","link":"https:\/\/feralpacket.org\/?p=635","title":{"rendered":"Multi-protocol Label Switching (MPLS) Notes"},"content":{"rendered":"

Multi-protocol Label Switching (MPLS)<\/span><\/p>\n

\nTraditional routing<\/p>\n

\n– Destination IP -> Next hop\n<\/p>\n

\nMPLS<\/p>\n

\n– Labels -> Next hop<\/p>\n

\n– No need to look to routing table\n<\/p>\n

<\/p>\n

<\/p>\n

<\/p>\n

DLCI -> Labels<\/p>\n

MPLS Architecture<\/span><\/p>\n

\u00a0– Labels<\/p>\n

\u00a0 \u00a0 \u00a0-> 32-bit value used for data propogation<\/p>\n

<\/p>\n

Label number -> 2^20<\/p>\n

Experimental bits<\/p>\n

\u00a0 \u00a0 \u00a0-> QoS<\/p>\n

\u00a0 \u00a0 \u00a0-> 8 possible values<\/p>\n

Bottom of Stack<\/p>\n

\u00a0 \u00a0 \u00a0-> 0 – More labels to follow<\/p>\n

\u00a0 \u00a0 \u00a0-> 1 – Last label<\/p>\n

TTL<\/p>\n

\u00a0 \u00a0 \u00a0-> Default is 255<\/p>\n

<\/p>\n

Terminology<\/span><\/p>\n

\u00a0– LSR<\/p>\n

\u00a0 \u00a0 \u00a0-> Label Switching Router<\/p>\n

\u00a0– LSP<\/p>\n

\u00a0 \u00a0 \u00a0-> Label Switched Path<\/p>\n

\u00a0 \u00a0 \u00a0-> The path a\u00a0labeled\u00a0packet takes to reach destination<\/p>\n

Label Switching Protocols<\/span><\/p>\n

\u00a0– TDP<\/p>\n

\u00a0 \u00a0 \u00a0-> Tag Distribution Protocol<\/p>\n

\u00a0 \u00a0 \u00a0-> Cisco Proprietary<\/p>\n

\u00a0 \u00a0 \u00a0-> Deprecated<\/p>\n

\u00a0 \u00a0 \u00a0-> Appears in the Troubleshooting section of the R&S lab<\/p>\n

\u00a0– LDP<\/p>\n

\u00a0 \u00a0 \u00a0-> Label Distribution Protocol<\/p>\n

\u00a0 \u00a0 \u00a0-> Open standard<\/p>\n

Forward Equivalency Class (FEC)<\/span><\/p>\n

\u00a0– A group of packets which receive similar treatment in terms of data forwarding<\/p>\n

Label Distribution Protocol<\/span><\/p>\n

\u00a0– Used for layer 2 purposes<\/p>\n

\u00a0 \u00a0 \u00a0-> To generate labels for all routes found in the routing table<\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -> Except for BGP routes<\/p>\n

\u00a0 \u00a0 \u00a0-> Distribute labels to neighbors<\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -> The labels a route generates are used by LDP neighbors<\/p>\n

<\/p>\n

Label Forwarding Information Base (LFIB)<\/p>\n

\u00a0– Used by CEF<\/p>\n

\u00a0<\/p>\n

Frame header has a protocol type file<\/p>\n

\u00a0– Code for MPLS packet<\/p>\n

\u00a0– Code for IP packet<\/p>\n

Packet with label<\/p>\n

\u00a0– Check LFIB<\/p>\n

Packet without label<\/p>\n

\u00a0– Check FIB<\/p>\n

A label for every route is listed in the FIB<\/p>\n

sh ip cef<\/span><\/p>\n

\u00a0– Will show the labels if LDP is enable<\/p>\n

R1 -> R2<\/p>\n

\u00a0– CEF lookup<\/p>\n

\u00a0– Push -> Imposing a label<\/p>\n

R2 -> R3<\/p>\n

\u00a0– LFIB -> Label lookup<\/p>\n

\u00a0– Swap -> Change label to next hop<\/p>\n

R3 -> R4<\/p>\n

\u00a0– LFIB -> Label lookup<\/p>\n

\u00a0– Swap -> Change label to next hop<\/p>\n

R4 -> Destination<\/p>\n

\u00a0– LFIB -> Label lookup<\/p>\n

\u00a0– Pop -> Remove the label<\/p>\n

\u00a0– CEF lookup<\/p>\n

The last hop router has to do two lookup<\/p>\n

\u00a0– To change to one lookup<\/p>\n

\u00a0 \u00a0 \u00a0-> R3 uses label “3” instead of 20<\/p>\n

\u00a0 \u00a0 \u00a0-> When R4 sees label “3”, it doesn’t do an LFIB looup<\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -> It Pops the label and goes straight to a CEF lookup<\/p>\n

\u00a0 \u00a0 \u00a0-> show command doesn’t show “3”, but “POP”<\/p>\n

Instructor comment, “MPLS requires the most structured teaching.”<\/p>\n

LDP uses UDP port 646 to find neighbors<\/p>\n

\u00a0– Discovery phase<\/p>\n

\u00a0 \u00a0 \u00a0-> 224.0.0.2 (all routers) UDP port 646<\/p>\n

\u00a0 \u00a0 \u00a0-> After finding a potential neighbor, a TCP session is established on TCP port 646<\/p>\n

\u00a0 \u00a0 \u00a0-> Hellos are sent every 5 seconds<\/p>\n

\u00a0 \u00a0 \u00a0-> Hold down timer is 15 seconds<\/p>\n

\u00a0– TCP Session<\/p>\n

\u00a0 \u00a0 \u00a0-> Once a TCP session is established<\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -> Keepalives are sent every 60 seconds<\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -> Hold down timer is 180 seconds<\/p>\n

\u00a0– After neighbor formation<\/p>\n

\u00a0 \u00a0 \u00a0-> Labels are exchanged<\/p>\n

\u00a0 \u00a0 \u00a0-> Kept in Label Information Base (LIB)<\/p>\n

\u00a0 \u00a0 \u00a0-> LIB contains all labels, but might not have the best path (route)<\/p>\n

\u00a0 \u00a0 \u00a0-> The best labels from the LIB are sent to the LFIB<\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -> The routing table is referenced to determine the exit interface<\/p>\n

<\/p>\n

<\/p>\n

<\/p>\n

LIB<\/p>\n

\u00a0– Locally generated label for 23.0.0.0<\/p>\n

\u00a0 \u00a0 \u00a0-> 20<\/p>\n

\u00a0 \u00a0 \u00a0-> 12.0.0.3 – 3<\/p>\n

\u00a0 \u00a0 \u00a0-> 23.0.0.3 – 3<\/p>\n

LFIB<\/p>\n

\u00a0in \u00a0| out \u00a0 \u00a0 next-hop<\/p>\n

\u00a020 | 3 \u00a0 \u00a0 \u00a0 \u00a0fa0\/0 -> 12.0.0.2<\/p>\n

<\/p>\n

Configuration<\/span><\/p>\n

\u00a01. Activate CEF (activated by default)<\/p>\n

\u00a02. Activate MPLS<\/p>\n

\u00a03. Activate LDP<\/p>\n

\u00a04. Configure LDP on the interfaces where neighbors can be found<\/p>\n

R1(config)# ip cef<\/span><\/p>\n

\u00a0mpls ip<\/span><\/p>\n

\u00a0 \u00a0 \u00a0-> Enabled if an interface is configured<\/p>\n

\u00a0mpls label protocol { ldp | tdp }<\/span><\/p>\n

\u00a0int s0\/0<\/span><\/p>\n

\u00a0 mpls ip<\/span><\/p>\n

“Always check CEF”<\/p>\n

\u00a0 \u00a0 \u00a0 -> During troubleshooting section of the R&S lab<\/p>\n

<\/p>\n

OSPF Autoconfig<\/span><\/p>\n

\u00a0– Configures MPLS on all interfaces configured for OSPF<\/p>\n

router ospf 1<\/span><\/p>\n

\u00a0mpls ldp autoconfig<\/span><\/p>\n

After MPLS and LDP is configured, LDP selects a router-id<\/p>\n

\u00a0– Manual<\/p>\n

\u00a0– Highest loopback IP address<\/p>\n

\u00a0– Highest physical interface IP address<\/p>\n

LDP starts sending “discovery hellos” to 224.0.0.2, UDP port 646<\/p>\n

\u00a0– Contains<\/p>\n

\u00a0 \u00a0 \u00a0-> Router-id (LDP)<\/p>\n

\u00a0 \u00a0 \u00a0-> Transport address<\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -> Used for TCP session<\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -> By default, the router-id is used<\/p>\n

Scenario -> The loopbacks of R1 and R2 can not be advertised in IGP<\/p>\n

\u00a0<\/p>\n

Solution 1 -> Change the LDP router-id to something reachable<\/p>\n

R1(config)# mpls ldp router-id { <interface> | <ip address> } [force]<\/span><\/p>\n

\u00a0 \u00a0 \u00a0-> Force is optional, but always use it<\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -> Without force, the LDP router-id will only change after the next reboot<\/p>\n

\u00a0 \u00a0 \u00a0-> Interface uses the IP address of the interface<\/p>\n

Solution 2 -> Change the transport IP address<\/p>\n

\u00a0 \u00a0 \u00a0– Interface specific command<\/p>\n

R1(config)# int s0\/0<\/span><\/p>\n

\u00a0mpls ldp discovery transport-address { <interface> | <ip address> }<\/span><\/p>\n

Discovery Timer<\/p>\n

R1(config)# mpls ldp discovery hello { interval | hello } <seconds><\/span><\/p>\n

TCP Keepalive Timer<\/p>\n

R1(config)# mpls ldp holddown <seconds><\/span><\/p>\n

<\/p>\n

Label Numbers<\/p>\n

\u00a0– 2^20<\/p>\n

\u00a0– But in Cisco, only 0 – 100000 are used<\/p>\n

Reserved Labels<\/p>\n

\u00a0– 0 – 15<\/p>\n

\u00a0 \u00a0 \u00a0-> 0 – explicit NULL<\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -> Used when you keep the experimental bit (Used for QoS)<\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -> Last router will have to do two lookups<\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0-> LFIB<\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0-> CEF<\/p>\n

\u00a0 \u00a0 \u00a0-> 3 – implicit NULL<\/p>\n

\u00a0<\/p>\n

To use explicit NULL (0)<\/p>\n

R1(config)# mpls ldp explicit-null<\/span><\/p>\n

To change the label range<\/p>\n

R1(config)# mpls label range <lower> <upper><\/span><\/p>\n

sh mpls label range<\/span><\/p>\n

mpls ldp advertise-label<\/span><\/p>\n

\u00a0– LDP, by default, generates the labels for every route in the routing table and advertises them to neighbors<\/p>\n

\u00a0– This behavior can be changed to control which labels (routes) are advertised and to which neighbors they can be advertised<\/p>\n

no mpls ldp advertise-labels<\/span><\/p>\n

mlps ldp advertise-labels for <acl> [to <peer acl>]<\/span><\/p>\n

\u00a0 \u00a0 \u00a0-> for <acl><\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -> For which routes labels are to be advertised<\/p>\n

\u00a0 \u00a0 \u00a0-> to <peer acl><\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 -> To which neighbors labels will be advertised<\/p>\n

Scenario -> On R1 and R2, advertise labels only for loopbacks.<\/p>\n

R1(config)# access-list 1 permit 1.1.1.1<\/span><\/p>\n

\u00a0access-list 1 permit 2.2.2.2<\/span><\/p>\n

\u00a0no mpls ldp advertise-labels<\/span><\/p>\n

\u00a0mpls ldp advertise-labels for 1<\/span><\/p>\n

The ACL must list all “routes” to be advertised<\/p>\n

Instructor comment, “LDP is a huge topic. \u00a0I highly recommend reading a book on LDP.”<\/p>\n

Verification:<\/span><\/p>\n

IOS:<\/span><\/p>\n

sh mpls int<\/span><\/p>\n

sh mpls ldp nei<\/span><\/p>\n

sh mpls forwarding-table<\/span><\/p>\n

sh mpls int vrf ABC<\/span><\/p>\n

sh mpls ldp nei vrf ABC<\/span><\/p>\n

sh mpls forwarding-table vrf ABC<\/span><\/p>\n

XR:<\/span><\/p>\n

sh mpls int<\/span><\/p>\n

sh mpls ldp nei<\/span><\/p>\n

sh mpls forwarding<\/span><\/p>\n

sh mpls forwarding vrf ABC<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

Multi-protocol Label Switching (MPLS)<\/p>\n","protected":false},"author":1,"featured_media":623,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[32,31],"class_list":["post-635","post","type-post","status-publish","format-standard","hentry","category-ccie","tag-mpls","tag-published"],"_links":{"self":[{"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts\/635","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=635"}],"version-history":[{"count":1,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts\/635\/revisions"}],"predecessor-version":[{"id":708,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts\/635\/revisions\/708"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/media\/623"}],"wp:attachment":[{"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=635"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=635"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=635"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}