21 mins read
OSPF Overload
1. Intro
OSPF Overload: configure the local routing device so that it appears to be overloaded. You might do this when you want the routing device to participate in OSPF routing, but do not want it to be used for transit traffic.
There is no overload bit, like we have in ISIS Overload. Instead, OSPF Overload will increase the link metrics on the impacted router. There are other important points that we will see in our topology and that we will highlight at the end of the post.
We will use the same OSPF topology that we used in other posts:
In this topology we will set configure OSPF Overload on R6 and observe the impact.
2. Initial state
### R6 config:
root@R6# show protocols ospf | display set
set protocols ospf area 0.0.0.0 area-range 17.8.0.0/16
set protocols ospf area 0.0.0.0 interface ge-0/0/1.0 interface-type p2p
set protocols ospf area 0.0.0.0 interface ge-0/0/1.0 metric 10
set protocols ospf area 0.0.0.0 interface ge-0/0/2.0 interface-type p2p
set protocols ospf area 0.0.0.0 interface ge-0/0/2.0 metric 10
set protocols ospf area 0.0.0.0 interface lo0.0
set protocols ospf area 0.0.0.2 nssa default-lsa default-metric 10
set protocols ospf area 0.0.0.2 nssa area-range 2.2.0.0/16
set protocols ospf area 0.0.0.2 area-range 17.28.0.0/16
set protocols ospf area 0.0.0.2 interface ge-0/0/3.0 interface-type p2p
set protocols ospf area 0.0.0.2 interface ge-0/0/3.0 metric 10
set protocols ospf area 0.0.0.2 interface ge-0/0/4.0 interface-type p2p
set protocols ospf area 0.0.0.2 interface ge-0/0/4.0 metric 10
root@R6# run show ospf overview
Instance: master
Router ID: 17.0.0.6
Route table index: 0
Area border router, AS boundary router, NSSA router
LSA refresh time: 50 minutes
Post Convergence Backup: Disabled
Area: 0.0.0.0
Stub type: Not Stub
Authentication Type: None
Area border routers: 2, AS boundary routers: 2
Neighbors
Up (in full state): 2
Area: 0.0.0.2
Stub type: Stub NSSA, Stub cost: 10
Authentication Type: None
Area border routers: 0, AS boundary routers: 1
Neighbors
Up (in full state): 2
Topology: default (ID 0)
Prefix export count: 0
Full SPF runs: 94
SPF delay: 0.200000 sec, SPF holddown: 5 sec, SPF rapid runs: 3
Backup SPF: Not Needed
root@R6# run show ospf interface ge-0/0/3.0 extensive
Interface State Area DR ID BDR ID Nbrs
ge-0/0/3.0 PtToPt 0.0.0.2 0.0.0.0 0.0.0.0 1
Type: P2P, Address: 17.28.14.1, Mask: 255.255.255.0, MTU: 1500, Cost: 10
Adj count: 1
Hello: 10, Dead: 40, ReXmit: 5, Stub NSSA
Auth type: None
Protection type: None
Topology default (ID 0) -> Cost: 10
root@R6# run show ospf database lsa-id 17.0.0.6 extensive
OSPF database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router *17.0.0.6 17.0.0.6 0x8000005f 141 0x22 0x83b7 96
bits 0x3, link count 6
id 17.0.0.3, data 17.8.4.2, Type PointToPoint (1)
Topology count: 0, Default metric: 10
id 17.8.4.0, data 255.255.255.0, Type Stub (3)
Topology count: 0, Default metric: 10
id 17.0.0.5, data 17.8.13.2, Type PointToPoint (1)
Topology count: 0, Default metric: 10
id 17.8.13.0, data 255.255.255.0, Type Stub (3)
Topology count: 0, Default metric: 10
id 17.0.0.6, data 255.255.255.255, Type Stub (3)
Topology count: 0, Default metric: 0
id 128.49.239.134, data 255.255.255.255, Type Stub (3)
Topology count: 0, Default metric: 0
Topology default (ID 0)
Type: PointToPoint, Node ID: 17.0.0.5
Metric: 10, Bidirectional
Type: PointToPoint, Node ID: 17.0.0.3
Metric: 10, Bidirectional
Gen timer 00:06:59
Aging timer 00:57:39
Installed 00:02:21 ago, expires in 00:57:39, sent 00:02:21 ago
Last changed 00:02:21 ago, Change count: 6, Ours
OSPF database, Area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
Router *17.0.0.6 17.0.0.6 0x80000065 141 0x20 0xa781 72
bits 0x3, link count 4
id 17.0.0.7, data 17.28.14.1, Type PointToPoint (1)
Topology count: 0, Default metric: 10
id 17.28.14.0, data 255.255.255.0, Type Stub (3)
Topology count: 0, Default metric: 10
id 17.0.0.8, data 17.28.15.1, Type PointToPoint (1)
Topology count: 0, Default metric: 10
id 17.28.15.0, data 255.255.255.0, Type Stub (3)
Topology count: 0, Default metric: 10
Topology default (ID 0)
Type: PointToPoint, Node ID: 17.0.0.8
Metric: 10, Bidirectional
Type: PointToPoint, Node ID: 17.0.0.7
Metric: 10, Bidirectional
Gen timer 00:08:33
Aging timer 00:57:39
Installed 00:02:21 ago, expires in 00:57:39, sent 00:02:21 ago
Last changed 00:02:21 ago, Change count: 4, Ours
Summary *17.0.0.6 17.0.0.6 0x80000003 2870 0x20 0xcb43 28
mask 255.255.255.255
Topology default (ID 0) -> Metric: 0
Gen timer 00:00:43
Aging timer 00:12:09
Installed 00:47:50 ago, expires in 00:12:10, sent 00:47:48 ago
Last changed 02:21:23 ago, Change count: 1, Ours### R7 output:
root@R7> show ospf database
OSPF database, Area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 17.0.0.6 17.0.0.6 0x80000065 211 0x20 0xa781 72
Router *17.0.0.7 17.0.0.7 0x80000068 2879 0x20 0x89e2 120
Router 17.0.0.8 17.0.0.8 0x80000066 2554 0x20 0x733a 132
Summary 10.0.1.0 17.0.0.6 0x80000005 211 0x20 0x27dc 28
Summary 10.0.2.0 17.0.0.6 0x80000005 211 0x20 0x1ce6 28
Summary 10.1.1.0 17.0.0.6 0x80000005 211 0x20 0x1be7 28
Summary 10.1.2.0 17.0.0.6 0x80000005 211 0x20 0x7483 28
Summary 10.1.3.0 17.0.0.6 0x80000005 211 0x20 0x698d 28
Summary 17.0.0.1 17.0.0.6 0x80000005 211 0x20 0xc23b 28
Summary 17.0.0.2 17.0.0.6 0x80000005 211 0x20 0x1dd5 28
Summary 17.0.0.3 17.0.0.6 0x80000005 211 0x20 0x4abb 28
Summary 17.0.0.4 17.0.0.6 0x80000005 211 0x20 0xa456 28
Summary 17.0.0.5 17.0.0.6 0x80000005 211 0x20 0x36cd 28
Summary 17.0.0.6 17.0.0.6 0x80000004 27 0x20 0xc944 28
Summary 17.8.0.0 17.0.0.6 0x80000004 211 0x20 0x787e 28
Summary 17.18.0.0 17.0.0.6 0x80000005 211 0x20 0xbc1c 28
NSSA 0.0.0.0 17.0.0.6 0x80000004 2360 0x20 0x20ee 36
NSSA *2.2.1.0 17.0.0.7 0x8000001d 2129 0x28 0x6fe9 36
NSSA *2.2.2.0 17.0.0.7 0x8000001d 1379 0x28 0x64f3 36
NSSA *2.2.3.0 17.0.0.7 0x8000001d 629 0x28 0x59fd 36
root@R7> show route table inet.0
inet.0: 51 destinations, 51 routes (51 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
0.0.0.0/0 *[OSPF/150] 02:22:58, metric 20, tag 0
> to 17.28.14.1 via ge-0/0/2.0
2.2.1.0/24 *[Static/5] 23:27:40
> to 17.28.18.2 via ge-0/0/4.0
2.2.2.0/24 *[Static/5] 23:27:40
> to 17.28.18.2 via ge-0/0/4.0
2.2.3.0/24 *[Static/5] 23:27:40
> to 17.28.18.2 via ge-0/0/4.0
10.0.1.0/24 *[OSPF/10] 00:03:55, metric 31
> to 17.28.14.1 via ge-0/0/2.0
10.0.2.0/24 *[OSPF/10] 00:03:55, metric 31
> to 17.28.14.1 via ge-0/0/2.0
10.1.1.0/24 *[OSPF/10] 00:03:55, metric 31
> to 17.28.14.1 via ge-0/0/2.0
10.1.2.0/24 *[OSPF/10] 00:03:55, metric 41
> to 17.28.14.1 via ge-0/0/2.0
10.1.3.0/24 *[OSPF/10] 00:03:55, metric 41
> to 17.28.14.1 via ge-0/0/2.0
10.2.1.0/24 *[Direct/0] 2d 03:27:44
> via ge-0/0/4.0
10.2.1.1/32 *[Local/0] 2d 03:27:44
Local via ge-0/0/4.0
10.2.2.0/24 *[OSPF/10] 23:42:57, metric 11
> to 17.28.17.2 via ge-0/0/3.0
10.2.3.0/24 *[OSPF/10] 23:42:57, metric 11
> to 17.28.17.2 via ge-0/0/3.0
17.0.0.1/32 *[OSPF/10] 00:03:55, metric 30
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.2/32 *[OSPF/10] 00:03:55, metric 40
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.3/32 *[OSPF/10] 00:03:55, metric 20
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.4/32 *[OSPF/10] 00:03:55, metric 30
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.5/32 *[OSPF/10] 00:03:55, metric 20
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.6/32 *[OSPF/10] 02:22:58, metric 10
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.7/32 *[Direct/0] 6d 21:07:36
> via lo0.0
17.0.0.8/32 *[OSPF/10] 23:42:57, metric 10
> to 17.28.17.2 via ge-0/0/3.0
17.8.0.0/16 *[OSPF/10] 00:03:55, metric 31
> to 17.28.14.1 via ge-0/0/2.0
17.18.0.0/16 *[OSPF/10] 00:03:55, metric 50
> to 17.28.14.1 via ge-0/0/2.0
17.28.5.0/24 *[Direct/0] 23:29:05
> via ge-0/0/1.0
17.28.5.2/32 *[Local/0] 23:29:05
Local via ge-0/0/1.0
17.28.14.0/24 *[Direct/0] 23:44:45
> via ge-0/0/2.0
17.28.14.2/32 *[Local/0] 23:44:45
Local via ge-0/0/2.0
17.28.15.0/24 *[OSPF/10] 23:42:57, metric 20
> to 17.28.14.1 via ge-0/0/2.0
to 17.28.17.2 via ge-0/0/3.0
17.28.17.0/24 *[Direct/0] 23:44:45
> via ge-0/0/3.0
17.28.17.1/32 *[Local/0] 23:44:45
Local via ge-0/0/3.0
17.28.18.0/24 *[Direct/0] 23:27:40
> via ge-0/0/4.0
17.28.18.1/32 *[Local/0] 23:27:40
Local via ge-0/0/4.0
17.28.19.0/24 *[OSPF/10] 23:28:09, metric 11
> to 17.28.17.2 via ge-0/0/3.0
17.28.21.0/24 *[Direct/0] 23:29:05
> via ge-0/0/5.0
17.28.21.2/32 *[Local/0] 23:29:05
Local via ge-0/0/5.03. Configure OSPF Overload
Let’s configure OSPF Overload and observe the impact:
### Configure OSPF Overload on R6:
root@R6# set protocols ospf overload
[edit]
root@R6# show | compare
[edit protocols ospf]
+ overload;
[edit]
root@R6# commit
commit complete
### No indication here that OSPF Overload is configured:
root@R6# run show ospf overview
Instance: master
Router ID: 17.0.0.6
Route table index: 0
Configured overload
Area border router, AS boundary router, NSSA router
LSA refresh time: 50 minutes
Post Convergence Backup: Disabled
Area: 0.0.0.0
Stub type: Not Stub
Authentication Type: None
Area border routers: 2, AS boundary routers: 2
Neighbors
Up (in full state): 2
Area: 0.0.0.2
Stub type: Stub NSSA, Stub cost: 10
Authentication Type: None
Area border routers: 0, AS boundary routers: 1
Neighbors
Up (in full state): 2
Topology: default (ID 0)
Prefix export count: 0
Full SPF runs: 95
SPF delay: 0.200000 sec, SPF holddown: 5 sec, SPF rapid runs: 3
Backup SPF: Not Needed
### Same here, no indication that OSPF Overload is configured.
root@R6# run show ospf database
OSPF database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 17.0.0.3 17.0.0.3 0x800000db 794 0x22 0x32f 96
Router 17.0.0.4 17.0.0.4 0x80000079 2117 0x22 0x5e08 132
Router 17.0.0.5 17.0.0.5 0x8000005b 1122 0x22 0x1163 96
Router *17.0.0.6 17.0.0.6 0x80000061 170 0x22 0x2528 96
Summary 10.1.1.0 17.0.0.3 0x8000001e 2671 0x22 0x787c 28
Summary 10.1.1.0 17.0.0.4 0x8000001f 2753 0x22 0xd414 28
Summary 10.1.2.0 17.0.0.3 0x8000001e 2586 0x22 0xd118 28
Summary 10.1.2.0 17.0.0.4 0x80000059 2571 0x22 0xf0c6 28
Summary 10.1.3.0 17.0.0.3 0x8000001e 2500 0x22 0xc622 28
Summary 10.1.3.0 17.0.0.4 0x80000059 2480 0x22 0xe5d0 28
Summary *10.2.1.0 17.0.0.6 0x80000024 786 0x22 0xe70d 28
Summary *10.2.2.0 17.0.0.6 0x80000023 786 0x22 0xde16 28
Summary *10.2.3.0 17.0.0.6 0x80000023 786 0x22 0xd320 28
Summary 17.0.0.1 17.0.0.3 0x8000001e 2243 0x22 0x20cf 28
Summary 17.0.0.1 17.0.0.4 0x8000001f 2389 0x22 0x7c67 28
Summary 17.0.0.2 17.0.0.3 0x8000001e 2157 0x22 0x7a6a 28
Summary 17.0.0.2 17.0.0.4 0x80000059 2298 0x22 0x9919 28
Summary *17.0.0.7 17.0.0.6 0x80000024 786 0x22 0x6189 28
Summary *17.0.0.8 17.0.0.6 0x80000023 786 0x22 0x5991 28
Summary 17.18.0.0 17.0.0.3 0x8000001f 2414 0x22 0x18b1 28
Summary 17.18.0.0 17.0.0.4 0x80000021 1844 0x22 0xeb8 28
Summary *17.28.0.0 17.0.0.6 0x8000001e 786 0x22 0xc40d 28
ASBRSum 17.0.0.1 17.0.0.3 0x80000020 877 0x22 0xede 28
ASBRSum 17.0.0.1 17.0.0.4 0x80000020 936 0x22 0x6c75 28
OSPF database, Area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
Router *17.0.0.6 17.0.0.6 0x80000067 80 0x20 0x49f1 72
Router 17.0.0.7 17.0.0.7 0x80000069 888 0x20 0x87e3 120
Router 17.0.0.8 17.0.0.8 0x80000067 562 0x20 0x713b 132
Summary *10.0.1.0 17.0.0.6 0x80000006 786 0x20 0xbe4e 28
Summary *10.0.2.0 17.0.0.6 0x80000006 786 0x20 0xb358 28
Summary *10.1.1.0 17.0.0.6 0x80000006 786 0x20 0xb259 28
Summary *10.1.2.0 17.0.0.6 0x80000006 786 0x20 0xcf4 28
Summary *10.1.3.0 17.0.0.6 0x80000006 786 0x20 0x1fe 28
Summary *17.0.0.1 17.0.0.6 0x80000006 786 0x20 0x5aac 28
Summary *17.0.0.2 17.0.0.6 0x80000006 786 0x20 0xb447 28
Summary *17.0.0.3 17.0.0.6 0x80000006 786 0x20 0xe32b 28
Summary *17.0.0.4 17.0.0.6 0x80000006 786 0x20 0x3cc7 28
Summary *17.0.0.5 17.0.0.6 0x80000006 786 0x20 0xcf3d 28
Summary *17.0.0.6 17.0.0.6 0x80000005 438 0x20 0xc745 28
Summary *17.8.0.0 17.0.0.6 0x80000005 786 0x20 0x10ef 28
Summary *17.18.0.0 17.0.0.6 0x80000006 786 0x20 0x548d 28
NSSA *0.0.0.0 17.0.0.6 0x80000005 752 0x20 0x1eef 36
NSSA 2.2.1.0 17.0.0.7 0x8000001e 138 0x28 0x6dea 36
NSSA 2.2.2.0 17.0.0.7 0x8000001d 2388 0x28 0x64f3 36
NSSA 2.2.3.0 17.0.0.7 0x8000001d 1638 0x28 0x59fd 36
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 1.1.0.0 17.0.0.1 0x80000006 1179 0x22 0x3e5b 36
Extern *2.2.0.0 17.0.0.6 0x80000007 259 0x22 0xf81 36
Extern 3.3.1.0 17.0.0.5 0x80000057 372 0x22 0x46f8 36
Extern 3.3.2.0 17.0.0.5 0x80000056 2622 0x22 0x3d02 36
Extern 3.3.3.0 17.0.0.5 0x80000056 1872 0x22 0x320c 36
Extern 4.4.1.0 17.0.0.3 0x80000057 711 0x22 0x3906 36
Extern 4.4.2.0 17.0.0.3 0x80000057 628 0x22 0x2e10 36
Extern 4.4.3.0 17.0.0.3 0x80000057 545 0x22 0x231a 36
### We can see the same Cost 10:
root@R6# run show ospf interface ge-0/0/3.0 extensive
Interface State Area DR ID BDR ID Nbrs
ge-0/0/3.0 PtToPt 0.0.0.2 0.0.0.0 0.0.0.0 1
Type: P2P, Address: 17.28.14.1, Mask: 255.255.255.0, MTU: 1500, Cost: 10
Adj count: 1
Hello: 10, Dead: 40, ReXmit: 5, Stub NSSA
Auth type: None
Protection type: None
Topology default (ID 0) -> Cost: 10
### This is where we can see the impact of configuring OSPF Overload
### The links now have the maximum metric:
root@R6# run show ospf database lsa-id 17.0.0.6 extensive
OSPF database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router *17.0.0.6 17.0.0.6 0x80000060 177 0x22 0x2727 96
bits 0x3, link count 6
id 17.0.0.3, data 17.8.4.2, Type PointToPoint (1)
Topology count: 0, Default metric: 65535
id 17.8.4.0, data 255.255.255.0, Type Stub (3)
Topology count: 0, Default metric: 10
id 17.0.0.5, data 17.8.13.2, Type PointToPoint (1)
Topology count: 0, Default metric: 65535
id 17.8.13.0, data 255.255.255.0, Type Stub (3)
Topology count: 0, Default metric: 10
id 17.0.0.6, data 255.255.255.255, Type Stub (3)
Topology count: 0, Default metric: 0
id 128.49.239.134, data 255.255.255.255, Type Stub (3)
Topology count: 0, Default metric: 0
Topology default (ID 0)
Type: PointToPoint, Node ID: 17.0.0.5
Metric: 65535, Bidirectional
Type: PointToPoint, Node ID: 17.0.0.3
Metric: 65535, Bidirectional
Gen timer 00:47:02
Aging timer 00:57:02
Installed 00:02:57 ago, expires in 00:57:03, sent 00:02:57 ago
Last changed 00:02:57 ago, Change count: 7, Ours
OSPF database, Area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
Router *17.0.0.6 17.0.0.6 0x80000066 177 0x20 0x4bf0 72
bits 0x3, link count 4
id 17.0.0.7, data 17.28.14.1, Type PointToPoint (1)
Topology count: 0, Default metric: 65535
id 17.28.14.0, data 255.255.255.0, Type Stub (3)
Topology count: 0, Default metric: 10
id 17.0.0.8, data 17.28.15.1, Type PointToPoint (1)
Topology count: 0, Default metric: 65535
id 17.28.15.0, data 255.255.255.0, Type Stub (3)
Topology count: 0, Default metric: 10
Topology default (ID 0)
Type: PointToPoint, Node ID: 17.0.0.8
Metric: 65535, Bidirectional
Type: PointToPoint, Node ID: 17.0.0.7
Metric: 65535, Bidirectional
Gen timer 00:47:02
Aging timer 00:57:02
Installed 00:02:57 ago, expires in 00:57:03, sent 00:02:57 ago
Last changed 00:02:57 ago, Change count: 5, Ours
Summary *17.0.0.6 17.0.0.6 0x80000004 425 0x20 0xc944 28
mask 255.255.255.255
Topology default (ID 0) -> Metric: 0
Gen timer 00:41:54
Aging timer 00:52:54
Installed 00:07:05 ago, expires in 00:52:55, sent 00:07:03 ago
Last changed 02:29:12 ago, Change count: 1, Ours
### R7 Output:
### As expected, the Area 2 database looks the same.
### (The database must be identical on all routers)
root@R7> show ospf database
OSPF database, Area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 17.0.0.6 17.0.0.6 0x80000066 549 0x20 0x4bf0 72
Router *17.0.0.7 17.0.0.7 0x80000069 649 0x20 0x87e3 120
Router 17.0.0.8 17.0.0.8 0x80000067 324 0x20 0x713b 132
Summary 10.0.1.0 17.0.0.6 0x80000006 549 0x20 0xbe4e 28
Summary 10.0.2.0 17.0.0.6 0x80000006 549 0x20 0xb358 28
Summary 10.1.1.0 17.0.0.6 0x80000006 549 0x20 0xb259 28
Summary 10.1.2.0 17.0.0.6 0x80000006 549 0x20 0xcf4 28
Summary 10.1.3.0 17.0.0.6 0x80000006 549 0x20 0x1fe 28
Summary 17.0.0.1 17.0.0.6 0x80000006 549 0x20 0x5aac 28
Summary 17.0.0.2 17.0.0.6 0x80000006 549 0x20 0xb447 28
Summary 17.0.0.3 17.0.0.6 0x80000006 549 0x20 0xe32b 28
Summary 17.0.0.4 17.0.0.6 0x80000006 549 0x20 0x3cc7 28
Summary 17.0.0.5 17.0.0.6 0x80000006 549 0x20 0xcf3d 28
Summary 17.0.0.6 17.0.0.6 0x80000005 201 0x20 0xc745 28
Summary 17.8.0.0 17.0.0.6 0x80000005 549 0x20 0x10ef 28
Summary 17.18.0.0 17.0.0.6 0x80000006 549 0x20 0x548d 28
Summary 128.49.228.245 17.0.0.6 0x80000006 549 0x20 0xfb90 28
Summary 128.49.239.134 17.0.0.6 0x80000005 112 0x20 0x7c7f 28
Summary 128.49.243.82 17.0.0.6 0x80000006 549 0x20 0x58d2 28
Summary 128.49.247.1 17.0.0.6 0x80000006 549 0x20 0xbbb2 28
Summary 128.49.247.24 17.0.0.6 0x80000005 549 0x20 0x74ed 28
Summary 128.49.247.27 17.0.0.6 0x80000005 549 0x20 0x1d2e 28
NSSA 0.0.0.0 17.0.0.6 0x80000005 515 0x20 0x1eef 36
NSSA *2.2.1.0 17.0.0.7 0x8000001d 2899 0x28 0x6fe9 36
NSSA *2.2.2.0 17.0.0.7 0x8000001d 2149 0x28 0x64f3 36
NSSA *2.2.3.0 17.0.0.7 0x8000001d 1399 0x28 0x59fd 36
### The LSA generated by R6 also looks the same.
### (The database must be identical on all routers)
root@R7> show ospf database lsa-id 17.0.0.6 extensive
OSPF database, Area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 17.0.0.6 17.0.0.6 0x80000066 560 0x20 0x4bf0 72
bits 0x3, link count 4
id 17.0.0.7, data 17.28.14.1, Type PointToPoint (1)
Topology count: 0, Default metric: 65535
id 17.28.14.0, data 255.255.255.0, Type Stub (3)
Topology count: 0, Default metric: 10
id 17.0.0.8, data 17.28.15.1, Type PointToPoint (1)
Topology count: 0, Default metric: 65535
id 17.28.15.0, data 255.255.255.0, Type Stub (3)
Topology count: 0, Default metric: 10
Topology default (ID 0)
Type: PointToPoint, Node ID: 17.0.0.8
Metric: 65535, Bidirectional
Type: PointToPoint, Node ID: 17.0.0.7
Metric: 65535, Bidirectional
Aging timer 00:50:40
Installed 00:09:19 ago, expires in 00:50:40, sent 00:09:19 ago
Last changed 00:09:19 ago, Change count: 17
Summary 17.0.0.6 17.0.0.6 0x80000005 212 0x20 0xc745 28
mask 255.255.255.255
Topology default (ID 0) -> Metric: 0
Aging timer 00:56:28
Installed 00:03:29 ago, expires in 00:56:28, sent 00:03:27 ago
Last changed 02:35:34 ago, Change count: 1
### We have max metric only on R6, for example R7 has same metrics.
root@R7> show ospf database lsa-id 17.0.0.7 extensive
OSPF database, Area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
Router *17.0.0.7 17.0.0.7 0x80000069 670 0x20 0x87e3 120
bits 0x2, link count 8
id 17.0.0.6, data 17.28.14.2, Type PointToPoint (1)
Topology count: 0, Default metric: 10
id 17.28.14.0, data 255.255.255.0, Type Stub (3)
Topology count: 0, Default metric: 10
id 17.0.0.8, data 17.28.17.1, Type PointToPoint (1)
Topology count: 0, Default metric: 10
id 17.28.17.0, data 255.255.255.0, Type Stub (3)
Topology count: 0, Default metric: 10
id 10.2.1.0, data 255.255.255.0, Type Stub (3)
Topology count: 0, Default metric: 1
id 17.28.18.0, data 255.255.255.0, Type Stub (3)
Topology count: 0, Default metric: 1
id 17.0.0.7, data 255.255.255.255, Type Stub (3)
Topology count: 0, Default metric: 0
id 128.49.239.108, data 255.255.255.255, Type Stub (3)
Topology count: 0, Default metric: 0
Topology default (ID 0)
Type: PointToPoint, Node ID: 17.0.0.8
Metric: 10, Bidirectional
Type: PointToPoint, Node ID: 17.0.0.6
Metric: 10, Bidirectional
Gen timer 00:38:49
Aging timer 00:48:49
Installed 00:11:10 ago, expires in 00:48:50, sent 00:11:08 ago
Last changed 02:35:44 ago, Change count: 19, OursInteresting to point out, only R6 will increase the metric, because only R6 is overloaded. Even though there is a link between R6 and R7, for this same link, R6 will advertise a max metric, but R7 will stick to the normal metric.
The implication is that this link is asymmetric now, max metric in R6-toR7 direction, and normal metric in R7-to-R6 direction.
### R7 routing table
### In the R7 Routing Table we can see the high metrics due to OPSF Overload:
root@R7> show route table inet.0
inet.0: 51 destinations, 51 routes (51 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
0.0.0.0/0 *[OSPF/150] 02:49:52, metric 20, tag 0
> to 17.28.14.1 via ge-0/0/2.0
2.2.1.0/24 *[Static/5] 23:54:34
> to 17.28.18.2 via ge-0/0/4.0
2.2.2.0/24 *[Static/5] 23:54:34
> to 17.28.18.2 via ge-0/0/4.0
2.2.3.0/24 *[Static/5] 23:54:34
> to 17.28.18.2 via ge-0/0/4.0
10.0.1.0/24 *[OSPF/10] 00:23:37, metric 65556
> to 17.28.14.1 via ge-0/0/2.0
10.0.2.0/24 *[OSPF/10] 00:23:37, metric 65556
> to 17.28.14.1 via ge-0/0/2.0
10.1.1.0/24 *[OSPF/10] 00:23:37, metric 65556
> to 17.28.14.1 via ge-0/0/2.0
10.1.2.0/24 *[OSPF/10] 00:23:37, metric 65566
> to 17.28.14.1 via ge-0/0/2.0
10.1.3.0/24 *[OSPF/10] 00:23:37, metric 65566
> to 17.28.14.1 via ge-0/0/2.0
10.2.1.0/24 *[Direct/0] 2d 03:54:38
> via ge-0/0/4.0
10.2.1.1/32 *[Local/0] 2d 03:54:38
Local via ge-0/0/4.0
10.2.2.0/24 *[OSPF/10] 1d 00:09:51, metric 11
> to 17.28.17.2 via ge-0/0/3.0
10.2.3.0/24 *[OSPF/10] 1d 00:09:51, metric 11
> to 17.28.17.2 via ge-0/0/3.0
17.0.0.1/32 *[OSPF/10] 00:23:37, metric 65555
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.2/32 *[OSPF/10] 00:23:37, metric 65565
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.3/32 *[OSPF/10] 00:23:37, metric 65545
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.4/32 *[OSPF/10] 00:23:37, metric 65555
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.5/32 *[OSPF/10] 00:23:37, metric 65545
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.6/32 *[OSPF/10] 02:49:52, metric 10
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.7/32 *[Direct/0] 6d 21:34:30
> via lo0.0
17.0.0.8/32 *[OSPF/10] 1d 00:09:51, metric 10
> to 17.28.17.2 via ge-0/0/3.0
17.8.0.0/16 *[OSPF/10] 00:23:37, metric 65556
> to 17.28.14.1 via ge-0/0/2.0
17.18.0.0/16 *[OSPF/10] 00:23:37, metric 65575
> to 17.28.14.1 via ge-0/0/2.0
17.28.5.0/24 *[Direct/0] 23:55:59
> via ge-0/0/1.0
17.28.5.2/32 *[Local/0] 23:55:59
Local via ge-0/0/1.0
17.28.14.0/24 *[Direct/0] 1d 00:11:39
> via ge-0/0/2.0
17.28.14.2/32 *[Local/0] 1d 00:11:39
Local via ge-0/0/2.0
17.28.15.0/24 *[OSPF/10] 1d 00:09:51, metric 20
> to 17.28.14.1 via ge-0/0/2.0
to 17.28.17.2 via ge-0/0/3.0
17.28.17.0/24 *[Direct/0] 1d 00:11:39
> via ge-0/0/3.0
17.28.17.1/32 *[Local/0] 1d 00:11:39
Local via ge-0/0/3.0
17.28.18.0/24 *[Direct/0] 23:54:34
> via ge-0/0/4.0
17.28.18.1/32 *[Local/0] 23:54:34
Local via ge-0/0/4.0
17.28.19.0/24 *[OSPF/10] 23:55:03, metric 11
> to 17.28.17.2 via ge-0/0/3.0
17.28.21.0/24 *[Direct/0] 23:55:59
> via ge-0/0/5.0
17.28.21.2/32 *[Local/0] 23:55:59
Local via ge-0/0/5.0It is important to point out, that the default route 0.0.0.0/0 still has metric 20, this is because the default-lsa was generated with a fixed metric on R6. So the total metric is 10 (default-lsa) + 10 (link cost) = metric 20:
set protocols ospf area 0.0.0.2 nssa default-lsa default-metric 10### R3 Output:
### Another observation is that External routes have the same metric:
root@R3> show route 2.2/16
inet.0: 60 destinations, 60 routes (60 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
2.2.0.0/16 *[OSPF/150] 02:56:59, metric 1, tag 0
> to 17.8.4.2 via ge-0/0/2.0
root@R3> show ospf database lsa-id 2.2.0.0 extensive
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 2.2.0.0 17.0.0.6 0x80000007 1378 0x22 0xf81 36
mask 255.255.0.0
Topology default (ID 0)
Type: 2, Metric: 1, Fwd addr: 0.0.0.0, Tag: 0.0.0.0
Aging timer 00:37:01
Installed 00:22:55 ago, expires in 00:37:02, sent 00:22:53 ago
Last changed 02:57:59 ago, Change count: 3
### Let's change the metric type on R7:
root@R7# set policy-options policy-statement TO-OSPF term 1 then external type 1
[edit]
root@R7# show | compare
[edit policy-options policy-statement TO-OSPF term 1 then]
+ external {
+ type 1;
+ }
[edit]
root@R7# commit
commit complete
### Now, with Type 1 external metric, the metric is increasing do to OSPF Overload:
root@R3> show route 2.2/16
inet.0: 60 destinations, 60 routes (60 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
2.2.0.0/16 *[OSPF/150] 00:00:40, , tag 0
> to 17.8.4.2 via ge-0/0/2.0
### Last but not least, OSPF Overload will not block traffic:
root@R3> show ospf database lsa-id 2.2.0.0 extensive
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 2.2.0.0 17.0.0.6 0x8000000c 45 0x22 0x7795 36
mask 255.255.0.0
Topology default (ID 0)
Type: 1, Metric: 65535, Fwd addr: 0.0.0.0, Tag: 0.0.0.0
Aging timer 00:59:15
Installed 00:00:44 ago, expires in 00:59:15, sent 00:00:44 ago
Last changed 00:00:44 ago, Change count: 10
root@R3> ping 17.0.0.7
PING 17.0.0.7 (17.0.0.7): 56 data bytes
64 bytes from 17.0.0.7: icmp_seq=0 ttl=63 time=3.575 ms
64 bytes from 17.0.0.7: icmp_seq=1 ttl=63 time=3.179 ms
64 bytes from 17.0.0.7: icmp_seq=2 ttl=63 time=3.723 ms
^C
--- 17.0.0.7 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max/stddev = 3.179/3.492/3.723/0.230 msExternal links with Type 2 metric will keep the original metric. Type 1 metric will still increase to max metric.
Also, even though there is no alternate path, the R6 router will still forward traffic even if Overloaded (as opposed to ISIS Overload where the router will not forward transit traffic).
4. OSPF Overload timeout
Let’s configure the timeout feature and see the impact:
### Configure OSPF Overload timeout on R6
### On R7 e still see the impact of OSPF Overload:
root@R7> show route 17.0/16 table inet.0
inet.0: 51 destinations, 51 routes (51 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
17.0.0.1/32 *[OSPF/10] 02:03:07, metric 65555
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.2/32 *[OSPF/10] 02:03:07, metric 65565
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.3/32 *[OSPF/10] 02:03:07, metric 65545
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.4/32 *[OSPF/10] 02:03:07, metric 65555
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.5/32 *[OSPF/10] 02:03:07, metric 65545
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.6/32 *[OSPF/10] 04:29:22, metric 10
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.7/32 *[Direct/0] 6d 23:14:00
> via lo0.0
17.0.0.8/32 *[OSPF/10] 1d 01:49:21, metric 10
> to 17.28.17.2 via ge-0/0/3.0
### Let's configure OSPF Overload timeout 300
root@R6# set protocols ospf overload timeout 300
[edit]
root@R6# show | compare
[edit protocols ospf overload]
+ timeout 300;
[edit]
root@R6# commit
commit complete
### Immediately we see Overload cleared.
### This is because more than 300 seconds have passed since OSPF process started.
root@R7> show route 17.0/16 table inet.0
inet.0: 51 destinations, 51 routes (51 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
17.0.0.1/32 *[OSPF/10] 00:00:07, metric 30
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.2/32 *[OSPF/10] 00:00:07, metric 40
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.3/32 *[OSPF/10] 00:00:07, metric 20
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.4/32 *[OSPF/10] 00:00:07, metric 30
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.5/32 *[OSPF/10] 00:00:07, metric 20
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.6/32 *[OSPF/10] 04:33:35, metric 10
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.7/32 *[Direct/0] 6d 23:18:13
> via lo0.0
17.0.0.8/32 *[OSPF/10] 1d 01:53:34, metric 10
> to 17.28.17.2 via ge-0/0/3.0
### Let's restart the routing process on R6:
root@R6> restart routing
Routing protocols process signalled but still running, waiting 28 seconds more
Routing protocols process started, pid 99503
### OSPF is reconverging:
root@R6> show ospf neighbor
Address Interface State ID Pri Dead
17.8.4.1 ge-0/0/1.0 ExStart 17.0.0.3 128 37
17.8.13.1 ge-0/0/2.0 ExStart 17.0.0.5 128 37
17.28.14.2 ge-0/0/3.0 Full 17.0.0.7 128 37
17.28.15.2 ge-0/0/4.0 ExStart 17.0.0.8 128 37
root@R6> show ospf neighbor
Address Interface State ID Pri Dead
17.8.4.1 ge-0/0/1.0 Full 17.0.0.3 128 35
17.8.13.1 ge-0/0/2.0 Full 17.0.0.5 128 34
17.28.14.2 ge-0/0/3.0 Full 17.0.0.7 128 34
17.28.15.2 ge-0/0/4.0 Full 17.0.0.8 128 32
### OSPF is Overloaded now:
root@R7> show route 17.0/16 table inet.0
inet.0: 51 destinations, 51 routes (51 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
17.0.0.1/32 *[OSPF/10] 00:01:08, metric 65555
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.2/32 *[OSPF/10] 00:01:19, metric 65565
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.3/32 *[OSPF/10] 00:01:08, metric 65545
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.4/32 *[OSPF/10] 00:01:19, metric 65555
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.5/32 *[OSPF/10] 00:01:19, metric 65545
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.6/32 *[OSPF/10] 00:01:25, metric 10
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.7/32 *[Direct/0] 6d 23:21:52
> via lo0.0
17.0.0.8/32 *[OSPF/10] 1d 01:57:13, metric 10
> to 17.28.17.2 via ge-0/0/3.0
### Automatically, after 300 seconds there is no more overload:
root@R7> show route 17.0/16 table inet.0
inet.0: 51 destinations, 51 routes (51 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
17.0.0.1/32 *[OSPF/10] 00:01:08, metric 30
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.2/32 *[OSPF/10] 00:01:08, metric 40
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.3/32 *[OSPF/10] 00:01:08, metric 20
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.4/32 *[OSPF/10] 00:01:08, metric 30
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.5/32 *[OSPF/10] 00:01:08, metric 20
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.6/32 *[OSPF/10] 00:05:53, metric 10
> to 17.28.14.1 via ge-0/0/2.0
17.0.0.7/32 *[Direct/0] 6d 23:26:20
> via lo0.0
17.0.0.8/32 *[OSPF/10] 1d 02:01:41, metric 10
> to 17.28.17.2 via ge-0/0/3.0We can conclude that the timeout feature works same as in ISIS Overload.
5. Conclusion
The main points to remember:
- There is no Overload bit in the LSA or the OSPF database (like in ISIS)
- OSPF Overload will instead increase link metric to max value of 65535.
- An OSPF Overloaded router will still forward traffic (as opposed to ISIS).
- Link metric will be asymmetric, max in one direction, normal metric in the other direction.
- LSA originated with a static metric, like default-lsa metric, will keep the configured value (no increase).
- External Type 2 metric will keep the configured value (External Type 1 metric will increase).
- Overload timeout is similar to ISIS.
If you want to see the Overload feature in ISIS and compare how they work, follow the link to ISIS Overload post.
External Resources: