Viewing the World in Binary

OSPF – EIGRP Redistribution

TOPOLOGY (snagged from our Multi Area Topology)

 

redist-topo

 

A1-R2 ——- ABR-VL-R8 ——– ASBR-A10R1 ———– ISP2

Area 1        Area 1 – 10(nssa)     AREA 10(nssa) – EIGRP 1          EIGRP 1

<—— One Way Redistribution EIGRP TO OSPF

Following config and route output is to study Route Propagation for network 50.50.16.0/20 and 50.50.32.0/20 from EIGRP Router to OSPF NSSA Area 10 and OSPF Area 1

! ISP2 Router with EIGRP Network

router eigrp 1
 network 50.50.16.0 0.0.15.255
 network 50.50.32.0 0.0.15.255
 network 70.71.72.4 0.0.0.3
 default-metric 10000 100 255 1 1500 ! [Speed/kbps] [delay/ms] [reliability] [load] [MTU]
 auto-summary ! Autosummarization – EIGRP installs the summary route with the next hop to Null0 for loop-prevention.

     50.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
C       50.50.16.0/20 is directly connected, FastEthernet1/0
C       50.50.32.0/20 is directly connected, FastEthernet2/0
D       50.0.0.0/8
is a summary, 01:26:55, Null0

! Auto summarization is enabled, directly connected route is installed with next hop as Null0 for loop-prevention.

     70.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
D       70.0.0.0/8 is a summary, 01:26:55, Null0
C       70.71.72.4/30 is directly connected, Serial0/0

! ASBR-A10R1 Not So Stubby Area (nssa) ASBR Router – OSPF Area 10 nssa/EIGRP 1 AS

router eigrp 1
network 70.71.72.4 0.0.0.3
auto-summary
!
router ospf 1
log-adjacency-changes
area 10 nssa
redistribute eigrp 1
network 10.10.1.4 0.0.0.3 area 10

1.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
O IA 1.1.1.4/30 [110/192] via 10.10.1.6, 00:02:27, Serial0/0
O IA 1.1.1.8/30 [110/128] via 10.10.1.6, 00:02:27, Serial0/0
O IA 1.1.30.0/24 [110/129] via 10.10.1.6, 00:02:27, Serial0/0
D 50.0.0.0/8 [90/2172416] via 70.71.72.5, 00:22:22, Serial0/1

! Internal EIGRP (route directly placed into EIGRP is classified as Internal EIGRP route) route Administrative Distance(AD) is 90, Feasible Distance is 2172416. See below for how we got that number.

70.0.0.0/30 is subnetted, 1 subnets
C 70.71.72.4 is directly connected, Serial0/1
101.0.0.0/32 is subnetted, 2 subnets
O IA 101.0.0.1 [110/65] via 10.10.1.6, 00:02:27, Serial0/0
O IA 101.0.0.2 [110/193] via 10.10.1.6, 00:02:27, Serial0/0
D 40.0.0.0/8 [90/2172416] via 70.71.72.5, 00:22:22, Serial0/1
10.0.0.0/30 is subnetted, 1 subnets
C 10.10.1.4 is directly connected, Serial0/0

ASBR-A10R1#sh ip eigrp topology 50.0.0.0
IP-EIGRP (AS 1): Topology entry for 50.0.0.0/8
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2172416
Routing Descriptor Blocks:
70.71.72.5 (Serial0/1), from 70.71.72.5, Send flag is 0x0
Composite metric is (2172416/28160), Route is Internal ! 28160 is Advertised Distance i.e metric peer advertised.
Vector metric:
Minimum bandwidth is 1544 Kbit
Total delay is 20100 microseconds
Reliability is 255/255
Load is 1/255
Minimum MTU is 1500
Hop count is 1

NOTE: Advertised Distance – Distance from neighbor to destination | Feasible Distance – Complete path from Source to Destination. Route’s where neighbors AD is less than our FD will not result in a loop.

Calculating Feasible Distance – The above `sh ip eigrp topology 50.0.0.0` command gives us Composite metric with Bandwidth and delay, we can now calculate the Feasible Distance. Command output shows 1 hop delay in micro seconds as 20100 and Minimum Bandwidth as 1544kb. We dont have to add delay as the destination is only 1 hop.

K2,K4,K5 by default have value 0 leading to this minimal metric formula.

metric = 256 * ( 10r7/1544 + 20100/10) = 256 * (6476.684 + 2010) = 2172591

So why the difference? what we got is 2172591 and EIGRP calculates it as 2172416

Actual Formula for computing is –

 

 

 

ABR-VL-R8 Area Border Router between NSSA and Area 1 (Area 10 is connected to Area 0 via Virtual Link)

router ospf 1
log-adjacency-changes
area 0 authentication message-digest
area 1 virtual-link 101.0.0.2 message-digest-key 1 md5 dracula
area 10 nssa
network 1.1.1.8 0.0.0.3 area 1
network 10.10.1.4 0.0.0.3 area 10
network 101.0.0.1 0.0.0.0 area 0

1.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
O 1.1.1.4/30 [110/128] via 1.1.1.10, 00:26:13, Serial0/0
C 1.1.1.8/30 is directly connected, Serial0/0
O 1.1.30.0/24 [110/65] via 1.1.1.10, 00:26:13, Serial0/0
O N2 50.0.0.0/8 [110/20] via 10.10.1.5, 00:00:02, Serial0/1

! N2 – Type 7 advertisements cross the NSSA and are converted back to type 5 LSAs at ABR. NSSA external routes show up as N1 or N2 instead of E1 or E2.

! [110/20] [OSPF Protocol Administrative Distance / Cost Metric] OSPF Cost Metric calculations are as below.

! OSPF Cost Metric – ‘Reference Bandwidth / Configured Bandwidth of interface in kbps’ : Reference Bandwidth is 100Mbs by default (100000000).


101.0.0.0/32 is subnetted, 2 subnets
C 101.0.0.1 is directly connected, Loopback0
O 101.0.0.2 [110/129] via 1.1.1.10, 00:00:02, Serial0/0
O N2 40.0.0.0/8 [110/20] via 10.10.1.5, 00:00:02, Serial0/1
10.0.0.0/30 is subnetted, 1 subnets
C 10.10.1.4 is directly connected, Serial0/1
192.0.0.0/30 is subnetted, 1 subnets
O 192.0.0.16 [110/192] via 1.1.1.10, 00:00:02, Serial0/0

`sh ip ospf database` Output from ABR-VL-R8 for Area 10

OSPF Router with ID (101.0.0.1) (Process ID 1)

Router Link States (Area 10)   <– Type-1 Router LS i.e intra-area LSA

Link ID ADV Router Age Seq# Checksum Link count
70.71.72.6 70.71.72.6 61 0x8000000B 0x007DC6 2
101.0.0.1 101.0.0.1 57 0x8000000C 0x00F3C2 2

Summary Net Link States (Area 10)  <– Type-3 Inter Area LS

Link ID ADV Router Age Seq# Checksum
0.0.0.0 101.0.0.1 155 0x80000004 0x009C30

Type-7 AS External Link States (Area 10)  

Link ID ADV Router Age Seq# Checksum Tag
40.0.0.0 70.71.72.6 59 0x80000009 0x00A2CD 0
50.0.0.0 70.71.72.6 59 0x80000009 0x002046 0

Type-5 AS External Link States

Link ID ADV Router Age Seq# Checksum Tag
40.0.0.0 101.0.0.1 46 0x80000001 0x008176 0
50.0.0.0 101.0.0.1 46 0x80000001 0x00FEEE 0

! A1-R2 (Area 1 Router with External Routes from NSSA)

1.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
C 1.1.1.4/30 is directly connected, Serial0/2
C 1.1.1.8/30 is directly connected, Serial0/1
C 1.1.30.0/24 is directly connected, FastEthernet1/0
O E2 50.0.0.0/8 [110/20] via 1.1.1.9, 00:03:10, Serial0/1

! E2 is default metric for External Routes – External cost of the path from the ASBR is only considered for calculation. (E1 – cost of path to reach ASBR internally is also added. Useful when internal routing should be included in path selection, E1 is the preffered path)


101.0.0.0/32 is subnetted, 2 subnets
O IA 101.0.0.1 [110/65] via 1.1.1.9, 00:29:14, Serial0/1
O IA 101.0.0.2 [110/65] via 1.1.1.6, 00:29:14, Serial0/2
O E2 40.0.0.0/8 [110/20] via 1.1.1.9, 00:03:10, Serial0/1
10.0.0.0/30 is subnetted, 1 subnets
O IA 10.10.1.4 [110/128] via 1.1.1.9, 00:09:13, Serial0/1
192.0.0.0/30 is subnetted, 1 subnets
O IA 192.0.0.16 [110/128] via 1.1.1.6, 00:03:15, Serial0/2

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

If we remove EIGRP network for 70.71.72.4/30 from ASBR-A10R1, we see the following:

ASBR-A10R1#
70.0.0.0/30 is subnetted, 1 subnets
C 70.71.72.4 is directly connected, Serial0/1
10.0.0.0/30 is subnetted, 1 subnets
C 10.10.1.4 is directly connected, Serial0/0

debug ip EIGRP 1

!! ASBR-A10R1 shows the following debug information and you can see the changes in route table.

ASBR-A10R1#
*Mar 1 01:03:59.227: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 70.71.72.5 (Serial0/1) is up: new a
djacency
*Mar 1 01:03:59.771: IP-EIGRP(Default-IP-Routing-Table:1): Processing incoming UPDATE packet
*Mar 1 01:03:59.775: IP-EIGRP(Default-IP-Routing-Table:1): 70.71.72.4/30 – do advertise out Serial0
/1
*Mar 1 01:04:00.075: IP-EIGRP(Default-IP-Routing-Table:1): Processing incoming UPDATE packet
*Mar 1 01:04:00.079: IP-EIGRP(Default-IP-Routing-Table:1): Int 40.0.0.0/8 M 2172416 – 1657856 51456
0 SM 28160 – 25600 2560
*Mar 1 01:04:00.083: IP-EIGRP(Default-IP-Routing-Table:1): route installed for 40.0.0.0 ()
*Mar 1 01:04:00.087: IP-EIGRP(Default-IP-Routing-Table:1): Int 50.0.0.0/8 M 2172416 – 1657856 51456
0 SM 28160 – 25600 2560
*Mar 1 01:04:00.091: IP-EIGRP(Default-IP-Routing-Table:1): route installed for 50.0.0.0 ()
*Mar 1 01:04:00.095: IP-EIGRP(Default-IP-Routing-Table:1): 70.71.72.4/30 – do advertise out Serial0
/1
*Mar 1 01:04:00.115: IP-EIGRP(Default-IP-Routing-Table:1): Processing incoming UPDATE packet
*Mar 1 01:04:00.119: IP-EIGRP(Default-IP-Routing-Table:1): Int 40.0.0.0/8 M 2172416 – 1657856 51456
0 SM 28160 – 25600 2560
*Mar 1 01:04:00.123: IP-EIGRP(Default-IP-Routing-Table:1): Int 50.0.0.0/8 M 2172416 – 1657856 51456
0 SM 28160 – 25600 2560

Default Seed Metrics

 

NOTE: EXPERIMENT WITH Redistribution from EIGRP to OSPF with Route Maps.

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November 5, 2008 Posted by | Protocols - OSPF | | Leave a comment