MPLS CSC
From IPFlow Netflow Collector
MPLS Carrier Supporting Carrier Example
This is a simple example of MPLS CSC configuration on Cisco routers (using Dynamips and GNS3).
Author: Christophe Fillot - 01-Nov-2007
| Table of contents |
Topology
Description
A client ISP wants to connect two entities (represented by CLI_PE1 and CLI_PE2/CLI_PE3 respectively) of its MPLS/VPN network through another MPLS/VPN backbone (CSC routers).
- The client ISP is seen as a VPN from the CSC backbone (VRF "VPN1" in CSC routers)
- The client ISP has its own VPNs, independently of the CSC backbone (VRF "VPNA" in CLI routers)
- The client ISP is 6PE-enabled, to show that it perfectly works through a CSC backbone.
Configuring CSC
This is very easy: on VRF interfaces going to CLI routers, just add "mpls ip":
CSC_PE1#sh run int fa1/0 Building configuration... Current configuration : 141 bytes ! interface FastEthernet1/0 description To CLI_PE1 ip vrf forwarding VPN1 ip address 100.0.1.1 255.255.255.252 duplex half mpls ip end
Then, check that the LDP adjacency is established:
CSC_PE1#sh mpls ldp nei vrf VPN1
Peer LDP Ident: 100.100.0.1:0; Local LDP Ident 100.0.1.1:0
TCP connection: 100.100.0.1.40052 - 100.0.1.1.646
State: Oper; Msgs sent/rcvd: 152/151; Downstream
Up time: 02:05:35
LDP discovery sources:
FastEthernet1/0, Src IP addr: 100.0.1.2
Addresses bound to peer LDP Ident:
100.0.1.2 100.100.0.1
To exchange routes between CSC_PE1 and CLI_PE1, and between CSC_PE2 and CLI_PE2, OSPF is used:
CSC_PE1#sh run | begin ^router ospf 200 router ospf 200 vrf VPN1 log-adjacency-changes redistribute bgp 65000 metric-type 1 subnets network 100.0.0.0 0.255.255.255 area 0 !
IOS configurations
IOS configurations for CSC backbone:
- CSC_P (http://www.ipflow.utc.fr/configs/MPLS_CSC/CSC_P.cfg)
- CSC_PE1 (http://www.ipflow.utc.fr/configs/MPLS_CSC/CSC_PE1.cfg)
- CSC_PE2 (http://www.ipflow.utc.fr/configs/MPLS_CSC/CSC_PE2.cfg)
IOS configurations for Client backbone:
- CLI_PE1 (http://www.ipflow.utc.fr/configs/MPLS_CSC/CLI_PE1.cfg)
- CLI_PE2 (http://www.ipflow.utc.fr/configs/MPLS_CSC/CLI_PE2.cfg)
- CLI_PE3 (http://www.ipflow.utc.fr/configs/MPLS_CSC/CLI_PE3.cfg)
Output of some commands
On CLI_PE1 (initiating the pings to CLI_PE3):
CLI_PE1#sh ip ro vrf VPNA
200.0.0.0/32 is subnetted, 3 subnets
C 200.0.0.1 is directly connected, Loopback100
B 200.0.0.2 [200/0] via 100.100.0.2, 01:19:24
B 200.0.0.3 [200/0] via 100.100.0.3, 01:06:39
CLI_PE1#sh ip cef vrf VPNA 200.0.0.3
200.0.0.3/32, version 8, epoch 0, cached adjacency 100.0.1.1
0 packets, 0 bytes
tag information set
local tag: VPN-route-head
fast tag rewrite with Fa0/0, 100.0.1.1, tags imposed: {24 20}
via 100.100.0.3, 0 dependencies, recursive
next hop 100.0.1.1, FastEthernet0/0 via 100.100.0.3/32
valid cached adjacency
tag rewrite with Fa0/0, 100.0.1.1, tags imposed: {24 20}
CLI_PE1#sh ipv6 route
LC FEC0:1000::1/128 [0/0]
via ::, Loopback0
B FEC0:1000::2/128 [200/0]
via ::FFFF:100.100.0.2, IPv6-mpls
B FEC0:1000::3/128 [200/0]
via ::FFFF:100.100.0.3, IPv6-mpls
L FF00::/8 [0/0]
via ::, Null0
CLI_PE1#sh ipv6 cef FEC0:1000::3
FEC0:1000::3/128
nexthop ::FFFF:100.100.0.3
fast tag rewrite with Fa0/0, 100.0.1.1, tags imposed: {24 21}
The first label (24) is used to reach 100.100.0.3 (Loopback0 of CLI_PE3):
CLI_PE1#sh ip cef 100.100.0.3
100.100.0.3/32, version 14, epoch 0, cached adjacency 100.0.1.1
0 packets, 0 bytes
tag information set, shared
local tag: 19
fast tag rewrite with Fa0/0, 100.0.1.1, tags imposed: {24}
via 100.0.1.1, FastEthernet0/0, 1 dependency
next hop 100.0.1.1, FastEthernet0/0
valid cached adjacency
tag rewrite with Fa0/0, 100.0.1.1, tags imposed: {24}
We can see below how labels 20 and 21 are handled by CLI_PE3:
CLI_PE3#sh mpls for Local Outgoing Prefix Bytes tag Outgoing Next Hop tag tag or VC or Tunnel Id switched interface 16 Pop tag 100.100.0.2/32 0 Fa0/0 100.0.23.1 17 Pop tag 100.0.2.0/30 0 Fa0/0 100.0.23.1 18 18 100.0.1.0/30 0 Fa0/0 100.0.23.1 19 19 100.100.0.1/32 0 Fa0/0 100.0.23.1 20 Aggregate 200.0.0.3/32[V] 5288 21 Aggregate FEC0:1000::3/128 1040
On CSC_PE1, we have the following MPLS forwarding table:
CSC_PE1#sh mpls for Local Outgoing Prefix Bytes tag Outgoing Next Hop tag tag or VC or Tunnel Id switched interface 16 Pop tag 10.10.0.0/32 0 Fa0/0 10.0.1.1 17 Pop tag 10.0.2.0/30 0 Fa0/0 10.0.1.1 18 17 10.10.0.2/32 0 Fa0/0 10.0.1.1 19 Aggregate 100.0.1.0/30[V] 3756 20 Pop tag 100.100.0.1/32[V] 17404 Fa1/0 100.0.1.2 21 19 100.0.2.0/30[V] 0 Fa0/0 10.0.1.1 22 20 100.0.23.0/30[V] 0 Fa0/0 10.0.1.1 23 21 100.100.0.2/32[V] 7703 Fa0/0 10.0.1.1 24 22 100.100.0.3/32[V] 4666 Fa0/0 10.0.1.1
Let's take a look on how label 24 is handled:
CSC_PE1#sh mpls for lab 24 det
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
24 22 100.100.0.3/32[V] 4666 Fa0/0 10.0.1.1
MAC/Encaps=14/22, MRU=1496, Tag Stack{17 22}
CA1368530000CA12685300008847 0001100000016000
VPN route: VPN1
No output feature configured
Per-packet load-sharing
We can see that label 24 is popped and replaced by 2 labels (17 and 22), corresponding to 100.100.0.3 in VRF "VPN1". On CLI_PE1, we saw that the labels used to reach 200.0.0.3 in vrf VPNA are "{24 20}", and that the labels used to reach FEC0:1000::3 are "{24 21}".
It means that when the packets leave CSC_PE1, there are 3 labels in the stack:
- {17 22 20} for 200.0.0.3 in vrf VPNA
- {17 22 21} for FEC0:1000::3
You can observe this in the PCAP file (to be used with Wireshark).
Traceroute Example:
CLI_PE1#trace vrf VPNA 200.0.0.3 Type escape sequence to abort. Tracing the route to 200.0.0.3 1 10.0.1.2 [MPLS: Labels 24/20 Exp 0] 12 msec 32 msec 28 msec 2 10.0.1.1 [MPLS: Labels 17/22/20 Exp 0] 20 msec 68 msec 4 msec 3 100.0.2.1 [MPLS: Labels 22/20 Exp 0] 72 msec 12 msec 24 msec 4 100.0.2.2 [MPLS: Labels 16/20 Exp 0] 24 msec 28 msec 24 msec 5 200.0.0.3 28 msec * 40 msec
PCAP captures
This PCAP capture (http://www.ipflow.utc.fr/configs/MPLS_CSC/mpls_csc.cap) shows the label stack in packets received by CSC_P, when pinging from CLI_PE1 to CLI_PE3.
Here are the screenshots from Wireshark:
- IPv4 ping (http://www.ipflow.utc.fr/configs/MPLS_CSC/wireshark_ping_v4.png)
- IPv6 ping (http://www.ipflow.utc.fr/configs/MPLS_CSC/wireshark_ping_v6.png)
Dynamips/Dynagen/GNS3 configuration
You can use this configuration file (http://www.ipflow.utc.fr/configs/MPLS_CSC/mpls_csc.net) directly with Dynagen or GNS3. Change the working directory and Cisco IOS image path to match your needs.
