Purpose
After you have configured the label-switched path (LSP), issued the show mpls lsp extensive command, and determined that there is an error, you might find that the error is not in the physical layer. Continue investigating the problem at the data link layer of the network.
Figure 12 illustrates the data link layer of the layered MPLS model.
Figure 12: Checking the Data Link Layer
With this layer, you must check the encapsulation mode, for example, Point-to-Point Protocol (PPP) or Cisco High-Level Data Link Control (HDLC); PPP options, for example, header encapsulation; frame check sequence (FCS) size; and whether keepalive frames are enabled or disabled. Also, check the ingress, egress, and transit routers.
Figure 13 illustrates the MPLS network used in this Find the appropriate term to place here instead of the word “chapter”..
Figure 13: MPLS Network Broken at the Data Link Layer
The network shown in Figure 13 is a fully meshed configuration where every directly connected interface can receive and send packets to every other similar interface. The LSP in this network is configured to run from ingress router R1, through transit router R3, to egress router R6. In addition, a reverse LSP is configured to run from R6 through R3 to R1, creating bidirectional traffic.
However, in this example, the LSP is down without a path in either direction, from R1 to R6 or from R6 to R1.
When you verify that the data link layer is not functioning correctly, you might find a mismatch with PPP or Cisco HDLC encapsulation, PPP options, or keepalive frames.
The cross shown in Figure 13 indicates where the LSP is broken because of a configuration error on ingress router R1 that prevents the LSP from traversing the network as expected.
To check the data link layer, follow these steps:
Typically, you use the show mpls lsp extensive command to verify the LSP. However for quick verification of the LSP state, use the show mpls lsp command. If the LSP is down, use the extensive option (show mpls lsp extensive) as a follow-up. If your network has numerous LSPs, you might consider specifying the name of the LSP, using the name option (show mpls lsp name name or show mpls lsp name name extensive).
To determine whether the LSP is up, enter the following command from the ingress router:
user@R1> show mpls lsp extensive
Ingress LSP: 1 sessions
10.0.0.6
From: 10.0.0.1 , State: Dn, ActiveRoute: 0, LSPname: R1-to-R6
ActivePath: (none)
LoadBalance: Random
Encoding type: Packet, Switching type: Packet, GPID: IPv4
Primary State: Dn
Will be enqueued for recomputation in 15 second(s).
140 Sep 30 12:01:12 CSPF failed: no route toward 10.0.0.6[26 times]
139 Sep 30 11:48:57 Deselected as active
138 Sep 30 11:48:56 CSPF failed: no route toward 10.0.0.6
137 Sep 30 11:48:56 Clear Call
136 Sep 30 11:48:56 CSPF: link down/deleted
10.1.36.1(R3.00/10.0.0.3)->10.1.36.2(R6.00/10.0.0.6)
135 Sep 30 11:48:56 ResvTear received
134 Sep 30 11:48:56 Down
133 Sep 30 11:48:56 CSPF failed: no route toward 10.0.0.6
132 Sep 30 11:48:56 10.1.13.2: No Route toward dest
[...Output truncated...]
Created: Sat Jul 10 18:18:44 2004
Total 1 displayed, Up 0, Down 1
Egress LSP: 0 sessions
Total 0 displayed, Up 0, Down 0
Transit LSP: 0 sessions
Total 0 displayed, Up 0, Down 0
The sample output from ingress router R1 shows the LSPs within which it participates. The ingress LSP is down, without a path from R1 to R6. Because a reverse LSP is configured in the network shown in Figure 13, we would expect an egress LSP session to be up. However, R1 does not have any egress LSPs, indicating that the LSP from R6 to R1 is not functioning.
From your network topology, determine the adjacent interfaces through which the LSP is meant to traverse, and examine the output for the encapsulation type, PPP options, FCS size, and whether keepalive frames are enabled or disabled
 |
Note: Before you proceed with this step, check the physical layer to ensure that the problem is not in the physical layer. |
To verify the functioning of adjacent interfaces, enter the following commands from the relevant routers:
user@R6> show interfaces so-0/0/3 extensive
Physical interface: so-0/0/3, Enabled, Physical link is Up
Interface index: 131, SNMP ifIndex: 27, Generation: 14
Link-level type: Cisco-HDLC , MTU: 4474, Clocking: Internal, SONET mode, Speed: OC3, Loopback: None,
FCS: 16 , Payload scrambler: Enabled
Device flags : Present Running
Interface flags: Link-Layer-Down Point-To-Point SNMP-Traps 16384
Link flags : Keepalives
Hold-times : Up 0 ms, Down 0 ms
Keepalive settings: Interval 10 seconds, Up-count 1, Down-count 3
Keepalive statistics:
Input : 0 (last seen: never)
Output: 357 (last sent 00:00:04 ago)
CoS queues : 4 supported
Last flapped : 2004-07-21 16:03:49 PDT (10w0d 07:01 ago)
Statistics last cleared: Never
Traffic statistics:
Input bytes : 203368873 0 bps
Output bytes : 186714992 88 bps
Input packets: 3641808 0 pps
Output packets: 3297569 0 pps
Input errors:
Errors: 0, Drops: 0, Framing errors: 0, Runts: 0, Giants: 0, Bucket drops: 0,
Policed discards: 1770, L3 incompletes: 0, L2 channel errors: 0, L2 mismatch timeouts: 0,
HS link CRC errors: 0, HS link FIFO overflows: 0
Output errors:
Carrier transitions: 1, Errors: 0, Drops: 0, Aged packets: 0, HS link FIFO underflows: 0,
MTU errors: 0
Queue counters: Queued packets Transmitted packets Dropped packets
0 best-effort 197012 197012 0
1 expedited-fo 0 0 0
2 assured-forw 0 0 0
3 network-cont 3100557 3100557 0
SONET alarms : None
SONET defects : None
SONET PHY: Seconds Count State
PLL Lock 0 0 OK
PHY Light 0 0 OK
SONET section:
BIP-B1 0 0
SEF 1 3 OK
LOS 1 1 OK
LOF 1 1 OK
ES-S 1
SES-S 1
SEFS-S 1
SONET line:
BIP-B2 0 0
REI-L 0 0
RDI-L 0 0 OK
AIS-L 0 0 OK
BERR-SF 0 0 OK
BERR-SD 0 0 OK
ES-L 1
SES-L 1
UAS-L 0
ES-LFE 0
SES-LFE 0
UAS-LFE 0
SONET path:
BIP-B3 0 0
REI-P 0 0
LOP-P 0 0 OK
AIS-P 0 0 OK
RDI-P 0 0 OK
UNEQ-P 0 0 OK
PLM-P 0 0 OK
ES-P 1
SES-P 1
UAS-P 0
ES-PFE 0
SES-PFE 0
UAS-PFE 0
Received SONET overhead:
F1 : 0x00, J0 : 0x00, K1 : 0x00, K2 : 0x00
S1 : 0x00, C2 : 0xcf, C2(cmp) : 0xcf, F2 : 0x00
Z3 : 0x00, Z4 : 0x00, S1(cmp) : 0x00
Transmitted SONET overhead:
F1 : 0x00, J0 : 0x01, K1 : 0x00, K2 : 0x00
S1 : 0x00, C2 : 0xcf, F2 : 0x00, Z3 : 0x00
Z4 : 0x00
Received path trace: R3 so-0/0/3
52 33 20 73 6f 2d 30 2f 30 2f 33 00 00 00 00 00 R3 so-0/0/3.. ...
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 0d 0a ................
Transmitted path trace: R6 so-0/0/3
52 36 20 73 6f 2d 30 2f 30 2f 33 00 00 00 00 00 R6 so-0/0/3 .....
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
HDLC configuration:
Policing bucket: Disabled
Shaping bucket : Disabled
Giant threshold: 4484, Runt threshold: 3
Packet Forwarding Engine configuration:
Destination slot: 0, PLP byte: 1 (0x00)
CoS transmit queue Bandwidth Buffer Priority Limit
% bps % bytes
0 best-effort 95 147744000 95 0 low none
3 network-control 5 7776000 5 0 low none
Logical interface so-0/0/3.0 (Index 71) (SNMP ifIndex 28) (Generation 16)
Flags: Device-Down Point-To-Point SNMP-Traps Encapsulation: Cisco-HDLC
Traffic statistics:
Input bytes : 406737746
Output bytes : 186714992
Input packets: 7283616
Output packets: 3297569
Local statistics:
Input bytes : 203368873
Output bytes : 186714992
Input packets: 3641808
Output packets: 3297569
Transit statistics:
Input bytes : 203368873 0 bps
Output bytes : 0 0 bps
Input packets: 3641808 0 pps
Output packets: 0 0 pps
Protocol inet, MTU: 4470, Generation: 46, Route table: 0
Flags: None
Addresses, Flags: Dest-route-down Is-Preferred Is-Primary
Destination: 10.1.36.0/30, Local: 10.1.36.2, Broadcast: 10.1.36.3, Generation: 38
Protocol iso, MTU: 4469, Generation: 47, Route table: 0
Flags: None
Protocol mpls, MTU: 4458, Generation: 48, Route table: 0
Flags: None
user@R3> show interfaces so-0/0/3
Physical interface: so-0/0/3, Enabled, Physical link is Up
Interface index: 131, SNMP ifIndex: 24
Link-level type: PPP , MTU: 4474, Clocking: Internal, SONET mode, Speed: OC3, Loopback: None, FCS: 16 ,
Payload scrambler: Enabled
Device flags : Present Running
Interface flags: Point-To-Point SNMP-Traps
Link flags : Keepalives
Keepalive settings: Interval 10 seconds, Up-count 1, Down-count 3
Keepalive: Input: 736827 (00:00:03 ago), Output: 736972 (00:00:05 ago)
LCP state: Opened
NCP state: inet: Opened, inet6: Not-configured, iso: Opened, mpls: Opened
CHAP state: Not-configured
CoS queues : 4 supported
Last flapped : 2004-07-21 16:08:01 PDT (10w5d 19:57 ago)
Input rate : 40 bps (0 pps)
Output rate : 48 bps (0 pps)
SONET alarms : None
SONET defects : None
Logical interface so-0/0/3.0 (Index 70) (SNMP ifIndex 51)
Flags: Point-To-Point SNMP-Traps Encapsulation: PPP
Protocol inet, MTU: 4470
Flags: None
Addresses, Flags: Is-Preferred Is-Primary
Destination: 10.1.36.0/30, Local: 10.1.36.1, Broadcast: 10.1.36.3
Protocol iso, MTU: 4470
Flags: None
Protocol mpls, MTU: 4458
Flags: None
Sample Output 1 from egress router R6 shows that there are no SONET alarms or defects (none), the states are all OK, and the path trace shows the distant end (R3 so-0.0.0), indicating that the physical link is up. However, the logical link is down, and the link-level type is Cisco HDLC.
Sample Output 2 from transit router R3 shows that the link-level type is PPP, indicating that the encapsulation types are mismatched, resulting in the LSP going down.
Depending on the error you encountered in your investigation, you must take the appropriate action to correct the problem. In the example below, the encapsulation types are mismatched.
To correct the error in this example, enter the following commands:
- [edit interfaces so-0/0/3]
- user@R1# show
- user@R1# delete encapsulation
- user@R1# show
- user@R1# commit
Sampel Output
[edit interfaces so-0/0/3]
user@R6# show
encapsulation cisco-hdlc;
unit 0 {
family inet {
address 10.1.36.2/30;
}
family iso;
family mpls;
}
[edit interfaces so-0/0/3]
user@R6# delete encapsulation
[edit interfaces so-0/0/3]
user@R6# show
unit 0 {
family inet {
address 10.1.36.2/30;
}
family iso;
family mpls;
}
[edit interfaces so-0/0/3]
user@R6# commit
commit complete
Meaning
The sample output from egress router R6 shows that the Cisco HDLC was incorrectly configured on interface so-0/0/3 which prevented the LSP from using the intended path. The problem was corrected when the encapsulation statement was deleted and the configuration committed.
After taking the appropriate action to correct the error, the LSP needs to be checked again to confirm that the problem in the data link layer has been resolved.
From the ingress, egress, and transit routers, verify that the LSP is up and traversing the network as expected:
user@R1> show mpls lsp extensive
Ingress LSP: 1 sessions
10.0.0.6
From: 10.0.0.1 , State: Up, ActiveRoute: 1 , LSPname: R1-to-R6
ActivePath: (primary)
LoadBalance: Random
Encoding type: Packet, Switching type: Packet, GPID: IPv4
*Primary State: Up
Computed ERO (S [L] denotes strict [loose] hops): (CSPF metric: 20)
10.1.13.2 S 10.1.36.2 S
Received RRO (ProtectionFlag 1=Available 2=InUse 4=B/W 8=Node 10=SoftPreempt):
10.1.13.2 10.1.36.2
145 Sep 30 12:25:01 Selected as active path
144 Sep 30 12:25:01 Record Route: 10.1.13.2 10.1.36.2
143 Sep 30 12:25:01 Up
142 Sep 30 12:25:01 Originate Call
141 Sep 30 12:25:01 CSPF: computation result accepted
140 Sep 30 12:24:32 CSPF failed: no route toward 10.0.0.6[74 times]
139 Sep 30 11:48:57 Deselected as active
138 Sep 30 11:48:56 CSPF failed: no route toward 10.0.0.6
137 Sep 30 11:48:56 Clear Call
136 Sep 30 11:48:56 CSPF: link down/deleted 10.1.36.1(R3.00/10.0.0.3)->10.1.36.2(R6.00/10.0.0.6)
[...Output truncated...]
Created: Sat Jul 10 18:18:43 2004
Total 1 displayed, Up 1 , Down 0
Egress LSP: 1 sessions
10.0.0.1
From: 10.0.0.6 , LSPstate: Up, ActiveRoute: 0
LSPname: R6-to-R1, LSPpath: Primary
Suggested label received: -, Suggested label sent: -
Recovery label received: -, Recovery label sent: -
Resv style: 1 FF, Label in: 3, Label out: -
Time left: 134, Since: Thu Sep 30 12:24:56 2004
Tspec: rate 0bps size 0bps peak Infbps m 20 M 1500
Port number: sender 6 receiver 39024 protocol 0
PATH rcvfrom: 10.1.13.2 (so-0/0/2.0) 7 pkts
Adspec: received MTU 1500
PATH sentto: localclient
RESV rcvfrom: localclient
Record route: 10.1.36.2 10.1.13.2 <self>
Total 1 displayed, Up 1, Down 0
Transit LSP: 0 sessions
Total 0 displayed, Up 0, Down 0
user@R6> show mpls lsp extensive
Ingress LSP: 1 sessions
10.0.0.1
From: 10.0.0.6, State: Up, ActiveRoute: 1, LSPname: R6-to-R1
ActivePath: (primary)
LoadBalance: Random
Encoding type: Packet, Switching type: Packet, GPID: IPv4
*Primary State: Up
Computed ERO (S [L] denotes strict [loose] hops): (CSPF metric: 20)
10.1.36.1 S 10.1.13.1 S
Received RRO (ProtectionFlag 1=Available 2=InUse 4=B/W 8=Node 10=SoftPreempt):
10.1.36.1 10.1.13.1
50 Sep 30 12:24:12 Selected as active path
49 Sep 30 12:24:12 Record Route: 10.1.36.1 10.1.13.1
48 Sep 30 12:24:12 Up
47 Sep 30 12:24:12 Originate Call
46 Sep 30 12:24:12 CSPF: computation result accepted
45 Sep 30 12:23:43 CSPF failed: no route toward 10.0.0.1[73 times]
44 Sep 30 11:48:12 Deselected as active
43 Sep 30 11:48:12 CSPF failed: no route toward 10.0.0.1
42 Sep 30 11:48:12 CSPF: link down/deleted 10.1.36.2(R6.00/10.0.0.6)->10.1.36.1(R3.00/10.0.0.3)
[...Output truncated...]
Created: Tue Aug 17 12:18:34 2004
Total 1 displayed, Up 1, Down 0
Egress LSP: 1 sessions
10.0.0.6
From: 10.0.0.1 , LSPstate: Up, ActiveRoute: 0
LSPname: R1-to-R6, LSPpath: Primary
Suggested label received: -, Suggested label sent: -
Recovery label received: -, Recovery label sent: -
Resv style: 1 FF, Label in: 3, Label out: -
Time left: 159, Since: Thu Sep 30 12:24:16 2004
Tspec: rate 0bps size 0bps peak Infbps m 20 M 1500
Port number: sender 19 receiver 44251 protocol 0
PATH rcvfrom: 10.1.36.1 (so-0/0/3.0) 4 pkts
Adspec: received MTU 1500
PATH sentto: localclient
RESV rcvfrom: localclient
Record route: 10.1.13.1 10.1.36.1 <self>
Total 1 displayed, Up 1, Down 0
Transit LSP: 0 sessions
Total 0 displayed, Up 0, Down 0
user@R3> show mpls lsp extensive Ingress LSP: 0 sessions Total 0 displayed, Up 0, Down 0 Egress LSP: 0 sessions Total 0 displayed, Up 0, Down 0 Transit LSP: 2 sessions 10.0.0.1 From: 10.0.0.6 , LSPstate: Up, ActiveRoute: 1 LSPname: R6-to-R1, LSPpath: Primary Suggested label received: -, Suggested label sent: - Recovery label received: -, Recovery label sent: 3 Resv style: 1 FF, Label in: 100176, Label out: 3 Time left: 143, Since: Thu Sep 30 12:21:25 2004 Tspec: rate 0bps size 0bps peak Infbps m 20 M 1500 Port number: sender 6 receiver 39024 protocol 0 PATH rcvfrom: 10.1.36.2 (so-0/0/3.0) 10 pkts Adspec: received MTU 1500 sent MTU 1500 PATH sentto: 10.1.13.1 (so-0/0/2.0) 9 pkts RESV rcvfrom: 10.1.13.1 (so-0/0/2.0) 9 pkts Explct route: 10.1.13.1 Record route: 10.1.36.2 <self> 10.1.13.1 10.0.0.6 From: 10.0.0.1 , LSPstate: Up, ActiveRoute: 1 LSPname: R1-to-R6, LSPpath: Primary Suggested label received: -, Suggested label sent: - Recovery label received: -, Recovery label sent: 3 Resv style: 1 FF, Label in: 100192, Label out: 3 Time left: 148, Since: Thu Sep 30 12:21:30 2004 Tspec: rate 0bps size 0bps peak Infbps m 20 M 1500 Port number: sender 19 receiver 44251 protocol 0 PATH rcvfrom: 10.1.13.1 (so-0/0/2.0) 9 pkts Adspec: received MTU 1500 sent MTU 1500 PATH sentto: 10.1.36.2 (so-0/0/3.0) 9 pkts RESV rcvfrom: 10.1.36.2 (so-0/0/3.0) 9 pkts Explct route: 10.1.36.2 Record route: 10.1.13.1 <self> 10.1.36.2 Total 2 displayed, Up 2, Down 0
user@R1> show configuration protocols mpls
label-switched-path R1-to-R6 {
to 10.0.0.6;
}
inactive: interface so-0/0/0.0;
inactive: interface so-0/0/1.0;
interface so-0/0/2.0;
user@R6> show configuration protocols mpls
label-switched-path R6-to-R1 {
to 10.0.0.1;
}
inactive: interface so-0/0/0.0;
inactive: interface so-0/0/1.0;
inactive: interface so-0/0/2.0;
interface so-0/0/3.0;
user@R3> show configuration protocols mpls
interface fxp0.0 {
disable;
}
inactive: interface so-0/0/0.0;
inactive: interface so-0/0/1.0;
interface so-0/0/2.0;
interface so-0/0/3.0;
Sample Outputs 1 and 2 from ingress router R1 and egress router R6, respectively, show that the LSP is now traversing the network along the expected path, from R1 through R3 to R6, and the reverse LSP, from R6 through R3 to R1.
Sample Output 3 from transit router R3 shows that there are two transit LSP sessions, one from R1 to R6 and the other from R6 to R1.
Sample Output 4 shows the interfaces that were deactivated on the ingress, egress, and transit routers, forcing the LSP to take the intended path. If these interfaces were not deactivated, even though the configuration is now correct, the LSP would still traverse the network through the alternate path.
