Finding the right IOU images can be a tricky thing to do, depending on what you are looking for. Things may look correct, but when you dig deeper down into it, you might not get the results you are looking for.
This all came about when discussing HSRP and IOU limitations with Maureen on a post about HSRP and ASICs.

IOU Images for Switches and for Routers

IOU images come in two flavors. We have Layer 2 images for switches, and we have router images. Calling the Layer 2 switch images is a bit of a misnomer because they can actually perform layer 3 functionality (such as having a layer 3 VLAN interface), so don’t worry too much about it being called layer 2 (or l2 in the filename). Don’t ask me to supply the IOU images, though, that’s your homework…

IOU Switch images

IOU images for switches are usually named i86bi_linux_l2-<image>-<date> such as:

• i86bi_linux_l2-ipbasek9-ms.jan24-2013-B
• i86bi_linux_l2-ipbasek9-ms.jan24-2013-team_track
• i86bi_linux_l2-ipbasek9-ms.may8-2-13-team_track
• i86bi_linux_l2-upk9-ms.june20_2012_golden_spike
• i86bi_linux_l2-adventerprise-ms.nov11-2013-team_track

Most of these are using the ipbasek9 image. But there are others out there.

IOU Router images

IOU images for routers follow pretty much the same naming format:

• i86bi_linux-adventerprisek9-ms.152-2.15.T
• i86bi_linux-adventerprisek9-ms.152-4.M1
• i86bi_linux-jk9s-ms.150-1.XJR111.358_120107
• i86bi_linux-p-ms.june20_2012_golden_spike

Needless to say that a router image is not the same as a switch image.

Not all IOU images are equal

So what’s the point of this anyway?

Take the following topology:

We have three switches and one host. The top two switches are set up with HSRP running for VLAN 10, with trunk ports between them and the third switch, that just has VLAN 10 configured. The VPCS host is connected to an access port that’s in VLAN 10. The configuration is as follows:

SW1#sh run int e0/0
Building configuration...

Current configuration : 103 bytes
!
interface Ethernet0/0
 switchport trunk encapsulation dot1q
 switchport mode trunk
 duplex auto
end

SW1#sh run int e0/1
Building configuration...

Current configuration : 103 bytes
!
interface Ethernet0/1
 switchport trunk encapsulation dot1q
 switchport mode trunk
 duplex auto
end

SW1#sh run int vlan 10
Building configuration...

Current configuration : 147 bytes
!
interface Vlan10
 ip address 10.10.1.2 255.255.255.0
 standby 10 ip 10.10.1.1
 standby 10 priority 150
 standby 10 preempt delay minimum 60
end

SW1#

SW2#sh run int e0/0
Building configuration...

Current configuration : 103 bytes
!
interface Ethernet0/0
 switchport trunk encapsulation dot1q
 switchport mode trunk
 duplex auto
end

SW2#sh run int e0/1
Building configuration...

Current configuration : 103 bytes
!
interface Ethernet0/1
 switchport trunk encapsulation dot1q
 switchport mode trunk
 duplex auto
end

SW2#sh run int vlan 10
Building configuration...

Current configuration : 109 bytes
!
interface Vlan10
 ip address 10.10.1.3 255.255.255.0
 standby 10 ip 10.10.1.1
 standby 10 priority 90
end

SW2#

SW3#sh run int e0/0
Building configuration...

Current configuration : 103 bytes
!
interface Ethernet0/0
 switchport trunk encapsulation dot1q
 switchport mode trunk
 duplex auto
end

SW3#sh run int e0/1
Building configuration...

Current configuration : 103 bytes
!
interface Ethernet0/1
 switchport trunk encapsulation dot1q
 switchport mode trunk
 duplex auto
end

SW3#sh run int e0/3
Building configuration...

Current configuration : 93 bytes
!
interface Ethernet0/3
 switchport access vlan 10
 switchport mode access
 duplex auto
end

SW3#

Nothing too hard here, but the image makes all the difference.

SW1#sh ver
Cisco IOS Software, Solaris Software (I86BI_LINUXL2-ADVENTERPRISE-M), Experimental Version 15.1(20131216:211730) [mmen 106]
Copyright (c) 1986-2013 by Cisco Systems, Inc.
Compiled Mon 16-Dec-13 13:50 by mmen

ROM: Bootstrap program is Linux

SW1 uptime is 1 hour, 5 minutes
System returned to ROM by reload at 0
System image file is "unix:/home/gns3/Documents/GNS3/images/i86bi_linux_l2-adventerprise-ms"

With this image, we don’t get any working HSRP. Both the top two switches think that they are the active switch:

SW1#sh standby vlan 10
Vlan10 - Group 10
  State is Active
    2 state changes, last state change 01:02:08
  Virtual IP address is 10.10.1.1
  Active virtual MAC address is 0000.0c07.ac0a (MAC In Use)
    Local virtual MAC address is 0000.0c07.ac0a (v1 default)
  Hello time 3 sec, hold time 10 sec
    Next hello sent in 1.904 secs
  Preemption enabled, delay min 60 secs
  Active router is local
  Standby router is unknown
  Priority 150 (configured 150)
  Group name is "hsrp-Vl10-10" (default)
SW1#

SW2#sh standby vlan 10
Vlan10 - Group 10
  State is Active
    2 state changes, last state change 01:03:07
  Virtual IP address is 10.10.1.1
  Active virtual MAC address is 0000.0c07.ac0a (MAC In Use)
    Local virtual MAC address is 0000.0c07.ac0a (v1 default)
  Hello time 3 sec, hold time 10 sec
    Next hello sent in 2.032 secs
  Preemption disabled
  Active router is local
  Standby router is unknown
  Priority 90 (configured 90)
  Group name is "hsrp-Vl10-10" (default)
SW2#

Debugging HSRP shows that the two are not talking to each other, even though CDP and ARP look fine:

SW1#sh cdp neigh
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone,
                  D - Remote, C - CVTA, M - Two-port Mac Relay

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
SW2              Eth 0/0           162             R S I  Linux Uni Eth 0/0
SW3              Eth 0/1           122             R S I  Linux Uni Eth 0/0
SW1#sh arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  10.10.1.1               -   0000.0c07.ac0a  ARPA   Vlan10
Internet  10.10.1.2               -   aabb.cc80.0100  ARPA   Vlan10
SW1#debug standby
HSRP debugging is on
SW1#
*May 23 07:39:26.362: HSRP: Vl10 Grp 10 Hello  out 10.10.1.2 Active  pri 150 vIP 10.10.1.1
SW1#
*May 23 07:39:29.211: HSRP: Vl10 Grp 10 Hello  out 10.10.1.2 Active  pri 150 vIP 10.10.1.1
SW1#
*May 23 07:39:31.624: HSRP: Vl10 Grp 10 Hello  out 10.10.1.2 Active  pri 150 vIP 10.10.1.1
SW1#
*May 23 07:39:34.614: HSRP: Vl10 Grp 10 Hello  out 10.10.1.2 Active  pri 150 vIP 10.10.1.1
SW1#
*May 23 07:39:37.568: HSRP: Vl10 Grp 10 Hello  out 10.10.1.2 Active  pri 150 vIP 10.10.1.1
SW1#
*May 23 07:39:40.328: HSRP: Vl10 Grp 10 Hello  out 10.10.1.2 Active  pri 150 vIP 10.10.1.1
SW1#
*May 23 07:39:43.090: HSRP: Vl10 Grp 10 Hello  out 10.10.1.2 Active  pri 150 vIP 10.10.1.1
SW1#

No HSRP traffic gets returned.

If we switch IOU images we do get a bit further:

SW1#sh ver
Cisco IOS Software, Solaris Software (I86BI_LINUXL2-IPBASEK9-M), Experimental Version 15.1(20130124:233217) [dstivers-jan24-2013-team_track 101]
Copyright (c) 1986-2013 by Cisco Systems, Inc.
Compiled Thu 24-Jan-13 16:17 by dstivers

ROM: Bootstrap program is Linux

SW2 uptime is 7 minutes
System returned to ROM by reload at 0
System image file is "unix:/home/gns3/Documents/GNS3/images/i86bi_linux_l2-ipbasek9-ms.jan2"

SW1#sh standby vlan 10
Vlan10 - Group 10
  State is Active
    2 state changes, last state change 00:01:36
  Virtual IP address is 10.10.1.1
  Active virtual MAC address is 0000.0c07.ac0a (MAC In Use)
    Local virtual MAC address is 0000.0c07.ac0a (v1 default)
  Hello time 3 sec, hold time 10 sec
    Next hello sent in 0.160 secs
  Preemption enabled, delay min 60 secs
  Active router is local
  Standby router is 10.10.1.3, priority 90 (expires in 10.592 sec)
  Priority 150 (configured 150)
  Group name is "hsrp-Vl10-10" (default)
SW1#

SW2#sh standby vlan 10
Vlan10 - Group 10
  State is Standby
    1 state change, last state change 00:01:21
  Virtual IP address is 10.10.1.1
  Active virtual MAC address is 0000.0c07.ac0a (MAC Not In Use)
    Local virtual MAC address is 0000.0c07.ac0a (v1 default)
  Hello time 3 sec, hold time 10 sec
    Next hello sent in 2.256 secs
  Preemption disabled
  Active router is 10.10.1.2, priority 150 (expires in 10.256 sec)
  Standby router is local
  Priority 90 (configured 90)
  Group name is "hsrp-Vl10-10" (default)
SW2#

So HSRP looks good from the viewpoint of the switches. However, not all is well from the VPCS guest:

VPCS2> ip 10.10.1.254 /24
Checking for duplicate address...
PC1 : 10.10.1.254 255.255.255.0

VPCS2> sh arp

arp table is empty

VPCS2> ping 10.10.1.2
10.10.1.2 icmp_seq=1 ttl=255 time=1.500 ms
10.10.1.2 icmp_seq=2 ttl=255 time=5.000 ms

VPCS2> ping 10.10.1.3
10.10.1.3 icmp_seq=1 ttl=255 time=3.500 ms
10.10.1.3 icmp_seq=2 ttl=255 time=4.000 ms

VPCS2> ping 10.10.1.1
10.10.1.1 icmp_seq=1 timeout
10.10.1.1 icmp_seq=2 timeout

VPCS2> sh arp

aa:bb:cc:80:04:00  10.10.1.2 expires in 65 seconds
aa:bb:cc:80:05:00  10.10.1.3 expires in 68 seconds
00:00:0c:07:ac:0a  10.10.1.1 expires in 70 seconds

VPCS2>

It can see that there is the HSRP VIF, but cannot reach it. SW3 also knows of the VIF:

SW3#sh mac address-table
          Mac Address Table
-------------------------------------------

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
  10    0000.0c07.ac0a    DYNAMIC     Et0/0
  10    0050.7966.6802    DYNAMIC     Et0/0
  10    aabb.cc80.0400    DYNAMIC     Et0/0
  10    aabb.cc80.0500    DYNAMIC     Et0/0
Total Mac Addresses for this criterion: 4
SW3#

So it goes to show that although things might look like they are working in IOU switches, downstream hosts might have a different idea about the network – so much so that things may not actually be reachable. Getting the correct IOU images is important. The people who enable us to get these images do a great job, but obviously cannot replicate 100% a device that relies on hardware to perform complex switching functions. There maybe functions that work in the first image used, that do not work in the second image I used. It can be a bit hit and miss.

If I do find an image that works in this scenario I will update the post, or if you know of one then please leave a comment below.