[Cake] dscp & tunneling

[Kevin Darbyshire-Bryant]

On 10/12/15 12:49, Dave Taht wrote:
> etags (or ctags) are friends here, as is cscope. I am in deep
> gratitude to toke for supplying me a pretty good working .emacs.d set
> of files for browsing code recently - I'd lost 20 years worth of
> accumulated tools when my lab got stolen and don't do enough software
> development today to justify sinking the time into making emacs sing
> and dance anymore. That said, I don't understand 90% of all the cool
> stuff he handed me...
>
> in the linux kernel tree, do a make TAGS. then in emacs it's esc->. to
> look up a symbol. There are ton of other things in cscope that are
> pretty amazing. vi has similar interfaces as do eclipse.
Well I'm beginning to get the vague whiff of a rat......

In iproute2 land 'iptunnel.c' is responsible for setting 'iph.tos'.

'ip tunnel' in openwrt land returns:

# ip tunnel
BusyBox v1.24.1 (2015-12-10 10:25:05 GMT) multi-call binary.

Usage: ip [OPTIONS] {address | route | link | rule} {COMMAND}

ip [OPTIONS] OBJECT {COMMAND}
where OBJECT := {address | route | link | rule}
OPTIONS := { -f[amily] { inet | inet6 | link } | -o[neline] }

First line gives a clue...this isn't real 'iproute2', this is busybox.

And a vaguely remember something going by on the openwrt commit list
about switching to 'busybox ip route' built-ins.

Does busybox understand the tos flag?

I can't prove it yet.  But it's one of those gut feels I get......


>
> On Thu, Dec 10, 2015 at 1:43 PM, Kevin Darbyshire-Bryant
> <kevin at darbyshire-bryant.me.uk> wrote:
>>
>> On 10/12/15 12:35, Kevin Darbyshire-Bryant wrote:
>>> On 10/12/15 12:22, Dave Taht wrote:
>>>> On Thu, Dec 10, 2015 at 1:09 PM, Kevin Darbyshire-Bryant
>>>> <kevin at darbyshire-bryant.me.uk> wrote:
>>>>
>>>>> the same test shows all those flows going in the best effort tin and
>>>>> nothing being split out according to dscp.  Things are split out
>>>>> correctly with ipv4.  Assuming that my installation of flent is doing
>>>>> the right thing (putting dscp on its outbound ipv6 packets) and knowing
>>>>> that both flent & cake handle the ipv4 version of the test correctly and
>>>>> that by the time 'cake' sees my tunnel it's all ipv4 outer packets
>>>>> anyway, this suggests dscp from inner ipv6 to outer ipv4 isn't taking
>>>>> place, at least for 6in4 'sit' tunnels :-(
>>>> Wireshark is your friend here.
>>> I shall befriend it once again :-)
>>>> It would not surprise me if dscp inherit had broken again, or, it was
>>>> borked on decapsulation. Not a widely tested feature, that.
>>> I'm only 'testing' the encapsulation side...ipv6 into router, router
>>> encapsulates into ipv6, cake then sits across 'eth0' the Internet facing
>>> interface and isn't classifying the flows - and I swear this used to work.
> I had it working 3 years back, yes, also.
>
>>>> I remember making it work several years ago, remember sort of seeing
>>>> the patches go upstream somewhere.... it was a long time ago.
>>> Is there anyone lurking on this list, with the time, who can help me
>>> with net/ipv6/sit.c?
>>>
>>> It looks like this is the relevant area:  Need to see what
>>> INET_ECN_encapsulate does (and where tos gets set)
>>>
>>>         if (ttl == 0)
>>>                 ttl = iph6->hop_limit;
>>>         tos = INET_ECN_encapsulate(tos, ipv6_get_dsfield(iph6));
>>>
>>>         if (ip_tunnel_encap(skb, tunnel, &protocol, &fl4) < 0) {
>>>                 ip_rt_put(rt);
>>>                 goto tx_error;
>>>         }
>>>
>>>         skb_set_inner_ipproto(skb, IPPROTO_IPV6);
>>>
>>>         err = iptunnel_xmit(NULL, rt, skb, fl4.saddr, fl4.daddr,
>>>                             protocol, tos, ttl, df,
>>>                             !net_eq(tunnel->net, dev_net(dev)));
>>>         iptunnel_xmit_stats(err, &dev->stats, dev->tstats);
>>>         return NETDEV_TX_OK;
>> Ahhh....further up...
>>
>>         if (tos == 1)
>>                 tos = ipv6_get_dsfield(iph6);
>>
>> and further up still...
>>
>> static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
>>                                      struct net_device *dev)
>> {
>>         struct ip_tunnel *tunnel = netdev_priv(dev);
>>         const struct iphdr  *tiph = &tunnel->parms.iph;
>>         const struct ipv6hdr *iph6 = ipv6_hdr(skb);
>>         u8     tos = tunnel->parms.iph.tos;
>>
>>
>> So how & who sets (or should be setting) iph.tos = 1?
>>
>> Rabbit hole, rabbit hole......
>>
>>
>>
>>
>>
>> _______________________________________________
>> Cake mailing list
>> Cake at lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/cake
>>


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