MPLS TE + CSPF

naive.naive · ‎02-27-2013

Got a simple question to ask (no equipment for me to test at the moment) hope it's alright..

Firstly, I know CSPF is enabled by default, is there any cli that can show that ?

Secondly, configured explicit path for the TE, and the 1st hop (hop 0) is directly connected interface, if the IGP (OSPF) goes down, will the tunnel still be up ?

RP/0/RP0/CPU0:CRS#sh mpls traffic-eng tunnels 99

Name: tunnel-te99 Destination: 172.16.1.1

Status:

Admin: up Oper: up Path: valid Signalling: connected

path option 10, type explicit Backup (Basis for Setup, path weight 100)

G-PID: 0x0800 (derived from egress interface properties)

Bandwidth Requested: 0 kbps CT0

Creation Time: Tue Nov 20 05:09:09 2012 (20w1d ago)

Config Parameters:

Bandwidth: 0 kbps (CT0) Priority: 7 7 Affinity: 0x0/0x2

Metric Type: TE (default)

Hop-limit: disabled

AutoRoute: enabled LockDown: disabled Policy class: not set

Forwarding-Adjacency: disabled

Loadshare: 0 equal loadshares

Auto-bw: disabled

Fast Reroute: Enabled, Protection Desired: Any

Path Protection: Not Enabled

History:

Tunnel has been up for: 20w1d (since Tue Nov 20 05:12:43 ESDT 2012)

Current LSP:

Uptime: 20w1d (since Tue Nov 20 05:12:43 ESDT 2012)

Reopt. LSP:

Last Failure:

LSP not signalled, identical to the [CURRENT] LSP

Date/Time: Wed Feb 22 05:08:17 ESDT 2013 [03:39:36 ago]

Path info (OSPF 10 area 2.0.0.1):

Hop0: 192.168.1.1

Hop1: 172.16.1.1

Nikhil Kapoor · ‎03-01-2013

HI Navie,

You may want to look at below outputs. This may answer what you are looking for.

Topology

********

P1 <---------------->P3 ( Running OSPF)

lo 2.2.2.2 lo0 5.5.5.5

Traffic Engineering running between P1 and P3 for simplicity.

P1#show mpls tra tu tun1

Name: P1_t1 (Tunnel1) Destination: 5.5.5.5

Status:

Admin: up Oper: up Path: valid Signalling: connected >>>> Oper status UP

path option 1, type dynamic (Basis for Setup, path weight 1)

With Dynamic option

*******************

P1#sh run int tu 1

Building configuration...

Current configuration : 269 bytes

!

interface Tunnel1

ip unnumbered Loopback0

load-interval 30

tunnel destination 5.5.5.5

tunnel mode mpls traffic-eng

tunnel mpls traffic-eng priority 7 7

tunnel mpls traffic-eng bandwidth 10

tunnel mpls traffic-eng path-option 1 dynamic

no routing dynamic

end

P1#

P1#show ip ro 5.5.5.5 >>>> Destination

Routing entry for 5.5.5.5/32

Known via "ospf 100", distance 110, metric 2, type intra area

Last update from 10.10.10.18 on GigabitEthernet1/0, 00:22:47 ago

Routing Descriptor Blocks:

* 10.10.10.18, from 5.5.5.5, 00:22:47 ago, via GigabitEthernet1/0

Route metric is 2, traffic share count is 1

P1#

I made OSPF IGP between P1 and P3 down.

P1#

*Mar 2 08:24:12.675: %OSPF-5-ADJCHG: Process 100, Nbr 5.5.5.5 on GigabitEthernet1/0 from FULL to DOWN, Neighbor Down: Dead timer expired

P1#

*Mar 2 08:24:26.639: %LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel1, changed state to down

P1#show mpls traffic-eng tunnels

Name: P1_t1 (Tunnel1) Destination: 5.5.5.5

Status:

Admin: up Oper: down Path: not valid Signalling: Down

path option 1, type dynamic

Config Parameters:

Bandwidth: 10 kbps (Global) Priority: 7 7 Affinity: 0x0/0xFFFF

Metric Type: TE (default)

AutoRoute: disabled LockDown: disabled Loadshare: 10 bw-based

auto-bw: disabled

History:

Tunnel:

Time since created: 10 minutes, 4 seconds

Time since path change: 1 minutes, 14 seconds

Number of LSP IDs (Tun_Instances) used: 27

Prior LSP:

ID: path option 1 [20]

Removal Trigger: path error

Last Error: PCALC:: No path to destination, 5.5.5.5

The same result I would expect for explicit path as well. Hence it looks like if the next hop or IGP adj between 2 routers is down TE tunnel will go down.

HTH

Nikhil

Akash Agrawal · ‎03-03-2013

Hi Navie,

To your first query to check whether CSPF or PCALC is enabled or not.

There is command "sh mpls traffic-eng topology path tunnel " for manual execution of Path Computation in Cisco IOS. This command will only give output of dynamic path based on PCALC computation.

To your second query:

I am not sure with the IOS-XR behaviour. I checked with IOS and below is my observation.

- Though router knows about next-hop address which is of connected device to reach the tail end, but it should be in TE topology databse also to check constraint specified in the TE tunnel.

- When OSPF is down on a link , router does not include this link into Opaque-area LSA and hence does not advertise Opaque-area LSA for this link to any router.
- This link also does not get added into MPLS traffic-eng database. (based on observation)
- Now when you configure a tunnel with path-option as dynamic, head end router runs CSPF or PCALC to know the shortest path to reach destination meeting all constrains specified and creates an ERO based on which PATH messgaes reached till Tail end router.
- In case of Explicit-path also Head end router runs PCALC to check if links specified in explicit route are meeting all constraints specified in TE tunnel or not. If not it will show an error and will not initiate PATH message.
- So say suppose you have added a link in explicit path which is not there in TE topology, it will give you error like "Last Error: PCALC:: No addresses to connect 172.31.12.2 to 172.31.23.3"

Topology
========

R1[.1]-----172.31.12.0/24----[2.]R2[.2]----172.31.23.0/24-----[.3]R3
| |
|-----------------------------172.31.13.0/24--------------------------------------|

tunnel is configured on R1 for R3

R1# sh runn int tunnel10
Building configuration...

Current configuration : 274 bytes
!
interface Tunnel10
ip unnumbered Loopback0
mpls traffic-eng tunnels
tunnel destination 3.3.3.3
tunnel mode mpls traffic-eng
tunnel mpls traffic-eng priority 7 7
tunnel mpls traffic-eng bandwidth 200
tunnel mpls traffic-eng path-option 1 explicit name R1-R2-R3
end

R1#

R1#sh ip expl name R1-R2-R3
PATH R1-R2-R3 (strict source route, path complete, generation 16)
1: next-address 172.31.12.2
2: next-address 172.31.23.3
R1#

CASE-I
======

OSPF is diabled between R1 and R2 due to password mismatch but R2 can advertises link address via R2-R3-R1 neighborship.

R1#sh mpls traffic tunnel tunnel 10

Name: R1_t10                              (Tunnel10) Destination: 3.3.3.3
Status:
    Admin: up         Oper: down   Path: not valid   Signalling: Down
    path option 1, type explicit R1-R2-R3

Config Parameters:
    Bandwidth: 200      kbps (Global) Priority: 7 7   Affinity: 0x0/0xFFFF
    Metric Type: TE (default)
    AutoRoute: disabled LockDown: disabled Loadshare: 200      bw-based
    auto-bw: disabled

Shortest Unconstrained Path Info:
    Path Weight: 10 (TE)
    Explicit Route: 172.31.13.3 3.3.3.3
History:
    Tunnel:
      Time since created: 1 hours, 51 minutes
      Time since path change: 20 seconds
      Number of LSP IDs (Tun_Instances) used: 268
    Prior LSP:
      ID: path option 1 [264]
      Removal Trigger: path verification failed
      Last Error: PCALC:: Explicit path has unknown address, 172.31.12.2 <<<<<<<<<<<<<<<<<
R1#

CASE-II
=======

OSPF is disabled between R2 and R3 due to password mismatch but R3 can advertises link address via R1-R3 neighborship.

R1#sh mpls traffic-eng tunnels tunnel 10

Name: R1_t10                              (Tunnel10) Destination: 3.3.3.3
Status:
    Admin: up         Oper: down   Path: not valid   Signalling: Down
    path option 1, type explicit R1-R2-R3

Config Parameters:
    Bandwidth: 200      kbps (Global) Priority: 7 7   Affinity: 0x0/0xFFFF
    Metric Type: TE (default)
    AutoRoute: disabled LockDown: disabled Loadshare: 200      bw-based
    auto-bw: disabled

Shortest Unconstrained Path Info:
    Path Weight: 10 (TE)
    Explicit Route: 172.31.13.3 3.3.3.3
History:
    Tunnel:
      Time since created: 1 hours, 36 minutes
      Time since path change: 33 seconds
      Number of LSP IDs (Tun_Instances) used: 242
    Prior LSP:
      ID: path option 1 [237]
      Removal Trigger: path error
      Last Error: PCALC:: No addresses to connect 172.31.12.2 to 172.31.23.3 <<<<<<<<<<<<<<<<<<
R1#

Opaque-area LSA contains Neighbor Address information as well

LS age: 677
Options: (No TOS-capability, DC)
LS Type: Opaque Area Link
Link State ID: 1.0.0.1
Opaque Type: 1
Opaque ID: 1
Advertising Router: 1.1.1.1
LS Seq Number: 80000008
Checksum: 0x5769
Length: 132
Fragment number : 1

    Link connected to Point-to-Point network
      Link ID : 3.3.3.3
      Interface Address : 172.31.13.1
      Neighbor Address : 172.31.13.3                    <<<<<<<
      Admin Metric : 10
      Maximum bandwidth : 1250000
      Maximum reservable bandwidth : 937500
      Number of Priority : 8
      Priority 0 : 937500      Priority 1 : 937500
      Priority 2 : 937500      Priority 3 : 937500
      Priority 4 : 937500      Priority 5 : 937500
      Priority 6 : 937500      Priority 7 : 937500
      Affinity Bit : 0x0
      IGP Metric : 10

Number of Links : 1

Muhammad Thanveer · ‎04-01-2013

good explanation akash.

Regards
Thanveer
"Everybody is genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is a stupid."