Confused with this config

Sa'ad

Hi all, can someone help me understand how there is 2 ip addresses on fastethernet 0 when there is only one ip configured on the interface.

This config is from production/live network.


User Access Verification

Password:
router>en

router>sh ver
Cisco Internetwork Operating System Software
IOS (tm) C1700 Software (C1700-Y-M), Version 12.3(16), RELEASE SOFTWARE (fc4)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2005 by cisco Systems, Inc.
Compiled Wed 24-Aug-05 00:28 by ssearch
Image text-base: 0x8000816C, data-base: 0x80A654A4

ROM: System Bootstrap, Version 12.0(3)T, RELEASE SOFTWARE (fc1)
ROM: C1700 Software (C1700-Y-M), Version 12.3(16), RELEASE SOFTWARE (fc4)

morrisFIN2622 uptime is 13 weeks, 2 days, 22 hours, 59 minutes
System returned to ROM by power-on
System image file is "flash:c1700-y-mz.123-16.bin"

cisco 1720 (MPC860T) processor (revision 0x501) with 36864K/12288K bytes of memo
ry.
Processor board ID JAD043309P8 (375851320, with hardware revision 0000
MPC860T processor: part number 0, mask 32
Bridging software.
X.25 software, Version 3.0.0.
1 FastEthernet/IEEE 802.3 interface(s)
1 Serial network interface(s)
WIC T1-DSU
32K bytes of non-volatile configuration memory.
8192K bytes of processor board System flash (Read/Write)

Configuration register is 0x2102
router>sh ip int brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0 208.51.59.97 YES NVRAM up up

Serial0 172.23.16.14 YES NVRAM up up

router>sh ip int brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0 208.51.59.97 YES NVRAM up up

Serial0 172.23.16.14 YES NVRAM up up

router>sh int s0
Serial0 is up, line protocol is up
Hardware is PQUICC with Fractional T1 CSU/DSU
Internet address is 172.23.16.14/30
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 200/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 101
Queueing strategy: weighted fair
Output queue: 0/1000/64/70 (size/max total/threshold/drops)
Conversations 0/17/256 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
Available Bandwidth 1158 kilobits/sec
5 minute input rate 1000 bits/sec, 3 packets/sec
5 minute output rate 2000 bits/sec, 3 packets/sec
17428343 packets input, 2029156893 bytes, 0 no buffer
Received 808632 broadcasts, 777 runts, 777 giants, 0 throttles
1608439 input errors, 220295 CRC, 712252 frame, 0 overrun, 0 ignored, 67587
6 abort
15019307 packets output, 3187725616 bytes, 0 underruns
0 output errors, 0 collisions, 979 interface resets
0 output buffer failures, 0 output buffers swapped out
167 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up


router>sh ip int brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0 208.51.59.97 YES NVRAM up up

Serial0 172.23.16.14 YES NVRAM up up

router>sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is 0.0.0.0 to network 0.0.0.0

216.174.202.0/29 is subnetted, 1 subnets
C 216.174.202.32 is directly connected, FastEthernet0
208.51.59.0/28 is subnetted, 1 subnets
C 208.51.59.96 is directly connected, FastEthernet0
172.23.0.0/30 is subnetted, 1 subnets
C 172.23.16.12 is directly connected, Serial0
S* 0.0.0.0/0 is directly connected, Serial0
[1/0] via 172.23.16.13

router>sh ip int brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0 208.51.59.97 YES NVRAM up up

Serial0 172.23.16.14 YES NVRAM up up

router>sh int fa0
FastEthernet0 is up, line protocol is up
Hardware is PQUICC_FEC, address is 0002.4b7d.8b10 (bia 0002.4b7d.8b10)
Internet address is 208.51.59.97/28
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s, 100BaseTX/FX
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:08, output 00:00:02, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
14521908 packets input, 3361297496 bytes
Received 380535 broadcasts, 0 runts, 0 giants, 0 throttles
4 input errors, 0 CRC, 4 frame, 0 overrun, 0 ignored
0 watchdog
0 input packets with dribble condition detected
17637604 packets output, 2188288583 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out
router>
router>sh ip int brief
Interface IP-Address OK? Method Status Prot
ocol
FastEthernet0 208.51.59.97 YES NVRAM up up

Serial0 172.23.16.14 YES NVRAM up up

router>sh arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 216.174.202.33 - 0002.4b7d.8b10 ARPA FastEthernet0
Internet 208.51.59.97 - 0002.4b7d.8b10 ARPA FastEthernet0
Internet 208.51.59.101 0 0009.5bc0.a2f3 ARPA FastEthernet0

router>exit

EdTheLad

Do a show running, is there a static route pointing to fa0 ?
i.e. ip route 216.174.202.33 255.255.255.248 fastethernet 0

Sa'ad

Thanks for your reply Ed, unfortunately I didn't have the enable password so I couldn't do the sh run command. Thanks for your help anyways.

rossonieri#1

hello,

ed is correct,
from your sh arp - its a possible secondary IP for other route,
because if someone did create an HSRP that MAC address will be different.

cheers.

Sa'ad

Thanks for your feedback Rosso, I believe you and Ed are right cuz I did a similar config on dynampis and I get the same result. I added a static route pointing to f0/0 and when I do the sh ip ro command I get the same result, the second ip looks as if its actually configured on the same interface. Thanks for figuring this out Ed/Rosso.