Re: IPv6 Link Local Addresses [was Re: Is 1111 1110 10 equal to 0xfe80 or 0x3fa?]

[Ole Troan <[e-mail]>]

Hi Gyan,

> I went through this test in the lab a few months ago about verifying across all Cisco platforms if you can specify non zero values in the all 0's field in the Link Local prefix hardcoding the prefix and if the OSPF neighbor would come up and it did come up in an all Cisco environment.  
> 
> So the main thing this draft accomplishes in my opinion and I think is necessary gap that it is fixing is interoperability between vendors for the use case of making the link local intuitive for the next hop by embedding the entire global unicast address into the iid & 54 bit 0s field.
> 
> Cisco happens to all the Link Local to be set and set all the 0s in the prefix fe80::/10 up to 64 which is a violation of the RFC but it does allow on all platforms and all codes.  I think we found that some unix flavors allow the same. 

Bias warning: I was heavily involved in one of the implementations you mention and the choice of how to implement link-local addresses.

That one vendor has chosen to allow the operator to chose if she wants to override the RFC behaviour, isn't in my view an argument for why we should change the standards.

Cheers,
Ole


> 
> So now the change to the RFC 4291 is making it official that it now can be allowed across all platforms to help with mixed vendor environments where you can now embedd the entire global unicast address into the station id making the default EUI64 station-id now intuitive.
> 
> https://datatracker.ietf.org/doc/html/draft-petrescu-6man-ll-prefix-len  
> **This is a copy/paste from a test I did in the lab a few months ago to prove my point**
> 
> I did a test in the lab for that one use case of making the default link local EUI64 more intuitive in the lab and Id id a worst case scenario test populating all the 16 bit nibbles and all hex digits within each nibble so no :: 0's compression on a Cisco IOS XE router running 16.x code and confirmed the OSPF neighbor still comes up even though the entire 54 bit all 0's field per the RFC is populated in effect violating the current RFC but because its like-like intra-vendor the OSPF adjacency forms.
>  
> So I have tested this concept and it works across all Cisco platforms IOS, XE, XR, NXOS that you can populate the entire 54 bit all 0's field.
>  
> So the big caveat with this and justification for this draft is "mix vendor" environment inter-operability" which is one of the reasons for the IETF and to have RFC's and standards that allows any device from any vendor to communicate that supports the RFC.     I think that is a MAJOR point to add to the justification behind the draft in the use cases where on a managed IPv6 network that the administrator can now hardcode the IPv6 address fully populating entire 54 bit subnet-id & station-id and routing protocols will now work and OSPF, ISIS, EIGRP adjacency can now work in a mix vendor environment.
>  
> R1
> ipv6 addr fe80:1111:1111:1111:1111:1111:1111:1111 link-local
>  
> R2
> ipv6 addr fe80:1111:1111:1111:1111:1111:1111:2222 link-local
>  
> R1#sh ipv6 ospf nei
>  
>             OSPFv3 Router with ID (1.1.1.1) (Process ID 6000)
>  
> Neighbor ID     Pri   State           Dead Time   Interface ID    Interface
> 2.2.2.2      1   FULL/DR         00:00:35    18              GigabitEthernet1/0/2
>  
> R1#sh ipv6 ospf int g1/0/2
> GigabitEthernet1/0/2 is up, line protocol is up 
>   Link Local Address FE80:1111:1111:1111:1111:1111:1111:1111, Interface ID 18
>   Area 2.2.2.2, Process ID 6000, Instance ID 0, Router ID 1.1.1.1
>   Network Type BROADCAST, Cost: 1
>   SHA-1 authentication SPI 666661, secure socket UP (errors: 0)
>   Transmit Delay is 1 sec, State BDR, Priority 1
>   Designated Router (ID) 2.2.2.2, local address FE80:1111:1111:1111:1111:1111:1111:2222
>   Backup Designated router (ID) 1.1.1.1, local address FE80:1111:1111:1111:1111:1111:1111:1111
>   Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
>     Hello due in 00:00:03
>   Graceful restart helper support enabled
>   Index 1/5/14, flood queue length 0
>   Next 0x0(0)/0x0(0)/0x0(0)
>   Last flood scan length is 2, maximum is 9
>   Last flood scan time is 0 msec, maximum is 1 msec
>   Neighbor Count is 1, Adjacent neighbor count is 1 
>     Adjacent with neighbor 2.2.2.2  (Designated Router)
>   Suppress hello for 0 neighbor(s)
>  
> R2#sh ipv6 ospf nei
>  
>             OSPFv3 Router with ID (2.2.2.2) (Process ID 6000)
>  
> Neighbor ID     Pri   State           Dead Time   Interface ID    Interface
> 1.1.1.1   1   FULL/BDR        00:00:37    18              GigabitEthernet1/0/2
>  
> R2#sh ipv6 ospf int g1/0/2
> GigabitEthernet1/0/2 is up, line protocol is up 
>   Link Local Address FE80:1111:1111:1111:1111:1111:1111:2222, Interface ID 18
>   Area 2.2.2.2, Process ID 6000, Instance ID 0, Router ID 104.255.32.2
>   Network Type BROADCAST, Cost: 1
>   SHA-1 authentication SPI 666661, secure socket UP (errors: 0)
>   Transmit Delay is 1 sec, State DR, Priority 1
>   Designated Router (ID) 2.2.2.2, local address FE80:1111:1111:1111:1111:1111:1111:2222
>   Backup Designated router (ID) 1.1.1.1, local address FE80:1111:1111:1111:1111:1111:1111:1111
>   Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
>     Hello due in 00:00:05
>   Graceful restart helper support enabled
>   Index 1/5/14, flood queue length 0
>   Next 0x0(0)/0x0(0)/0x0(0)
>   Last flood scan length is 0, maximum is 7
>   Last flood scan time is 0 msec, maximum is 1 msec
>   Neighbor Count is 1, Adjacent neighbor count is 1 
>     Adjacent with neighbor 1.1.1.1  (Backup Designated Router)
>   Suppress hello for 0 neighbor(s)
> 
> 
> On Tue, Jun 11, 2019 at 4:44 AM Ole Troan <[e-mail]> wrote:
> >> This means that link local addresses have a 10 bit prefix (1111111010) followed by 54 bits of zeros.  That is it, nothing more.   Address with different prefixes or with a 1111111010 prefix followed by non-zero 54 bits are not link local addresses.
> >> 
> >> This is not ambiguous.  
> > 
> > So if an application asks my implementation to send a packet addressed to fe80:1::1 out a particular link what should the implementation do with it? It seems like there are only 3 choices:
> > 
> >   1. Run ND on that link to see if it can find a neighbor there with that address to send the packet to.
> > 
> >   2. Send the packet to the current default router.
> > 
> >   3. Something else (what?).
> > 
> > I had though 1. was the answer since that is what is done with packets addressed to link-local unicast destinations (which is what that address is according to RFC4191 section 2.4), but that now seems to be ambiguous.
> 
> Let me illustrate with a typical per-interface FIB:
> 
>  fe80::/10 -> drop
>  fe80::/64 -> glean
>  fe80::abcd -> neighbor abcd
> 
> Cheers,
> Ole
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> 
> -- 
> Gyan S. Mishra
> IT Network Engineering & Technology 
> Verizon Communications Inc. (VZ)
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