Router - Cisco IPv6 IOS Versions

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Known working versions of IOS

Router IOS Version Image Name Connection Who Status
837 12.3 c837-k9o3sy6-mz.123-11.T10.bin PPPoA Nhumfrey ✓ Working
887 15.0 c880data-universalk9-mz.150-1.M9.bin PPPoA Nhumfrey ✗ IPV6CP being rejected
887 15.1 c880-advipservicesk9-mz.151-4.M5.bin PPPoA Nhumfrey ✓ Working
1841 12.4 c1841-advipservicesk9-mz.124-9.T5.bin PPPoE NetworkString ✓ Working (Using the additional config noted here)
1841 15.1 c1841-adventerprisek9-mz.151-4.M9.bin PPPoE Cmat100 ✓ Working (Using the additional config noted here)

Also, a customer has reported in July 2013:

✗ Not working: Firmware Source File Name (version)

Modem FW Version: 100819_1343-4.02L.03.A2pv6C032.d23b 
Modem PHY Version: A2pv6C032.d23b  

✓ Working:

Firmware	Source	 File Name (version) 
VDSL	        default  flash:vdsl.bin (10)  
Modem FW Version:	120910_1737-4.02L.03.A2pv6C035l.d23j 
Modem PHY Version:	A2pv6C035l.d23j

Routing IPv6 over PPP

If you are having trouble trying to get IPv6 to route over PPP, it might be because the version of IOS you are using doesn't support it.

This can be confirmed by turning on debugging of PPP negotiation:

 debug ppp negotiation

If when the connection is being established, you see this:

 Vi2 IPV6CP: I CONFREQ [UNKNOWN] id 0 len 14
 Vi2 IPV6CP:    (0x010A020397FFFE168000)
 Vi2 LCP: O PROTREJ [Open] id 4 len 20 protocol IPV6CP (0x01000010010A020397FFFE168000)
 Vi2 PPP: Outbound ipv6 packet dropped, NCP not negotiated
 Vi2 PPP: Outbound ipv6 packet dropped, NCP not negotiated

Then you will need to change to a version of IOS with the "advanced IP services" feature set. It looks like the basic IOS feature set does not support IPV6CP.

TCP window scaling Bug

Taken from:

Some customers running native IPv6 on a Cisco 877 router have seen a huge disparity between IPv4 and IPv6 speeds. IPv6 file transfers are about 10 times slower than IPv4 transfers!

It turns out to be a Cisco IOS bug; once the IPv6 stateful firewall (inspect) has been disabled, IPv6 should run at full speed.

It is Cisco bug CSCtb10776 (Inspection drops NIC-segmented packets when WScale is on). It can also be worked around by disabling TCP window scaling on the affected hosts, but that can have performance implications of its own. It has been fixed in IOS versions:

  • 15.1(0.18)T
  • 12.4(25b)M0.13
  • 15.0(1)M1.2