Now Broadband giving me an unroutable IPv4 address

[David_Evans]

I've been happily sitting for years on a Now Broadband connection with my own router running Openwrt, but then I was suddenly given a 100.126.X.X IP address, which is a 'shared address space' IP so it won't route on the public internet. The IPv6 still seems to work, but that obviously is not the same as having IPv4 access. Same happens when I put the Now hub back on.

I phoned Now Broadband tech support, but they could only run through their script and decide to call out an Openreach engineer. I tried to explain that this was unlikely to help, but that was their only option.

Rummaging around, it looks like Sky have been rolling out Map-t, which might explain it, but I can't see anyone having the symptoms I've been getting. Anyone got any ideas? Is there a way to contact someone at Now who you can actually have a conversation about this with?

[TimmyBGood]

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@David_Evans wrote:

I've been happily sitting for years on a Now Broadband connection with my own router running Openwrt, but then I was suddenly given a 100.126.X.X IP address, which is a 'shared address space' IP so it won't route on the public internet. 

The unroutable address spaces are 

• 10.0.0.0 – 10.255.255.255 (10.0.0.0/8)
• 172.16.0.0 – 172.31.255.255 (172.16.0.0/12)
• 192.168.0.0 – 192.168.255.255 (192.168.0.0/16)

100.126.X.X should be entirely legitimate.

Rummaging around, it looks like Sky have been rolling out Map-t, which might explain it, but I can't see anyone having the symptoms I've been getting. 

Map-T is only in effect on circuits with a Sky Max Hub because that hardware is required at the subscriber end.

---

Edit: it's space covered by https://datatracker.ietf.org/doc/html/rfc6598 for use in CGNAT

[David_Evans]

Thanks - you're right, it's an address used for CGNAT or MAP-T (which is a new approach supposed to be better than CGNAT). Anything inside 100.64.0.0/10 can be treated as private and non-routable.

Anyone any ideas why Now might be doing this, how to deal with it, or how to get in touch with them?

[David_Evans]

The good news is that I managed to get my connection working. The bad news is that NOW Broadband were no help at all, and it is only because I'm using OpenWRT that I managed to get it working.

As reported in June this year, Sky are rolling out MAP-T, which is a solution similar to CGNAT:

https://www.ispreview.co.uk/index.php/2024/06/isp-sky-broadband-uk-deploying-ip-address-sharing-via-...

Having phoned NOW support, their only option was to send an Openreach engineer. He was very professional and helpful, but the issue was not something he was trained on. He phoned NOW who said no idea phone Sky. He phoned Sky, and they were deeply confused as to why I'd been moved onto this configuration. He seemed to think they were moving me back (although that hasn't happened).

Meanwhile, because of the 100.126.X.X address assigned I thought I would see if I could set up my own router with MAP-T. The short version is that having installed the software it seems to work very well. OpenWRT is a brilliant peice of software, and the packages you can install cover such a vast array of situations and services. Plugging my NOW router back in confirms that still doesn't work.

The icing on the cake is that I had a follow-up call from the NOW support call centre. Their advice to me was to use my NOW router 😂

I did attempt to explain to them that this would result in me having no Internet access, but it's not as though they had any way to respond to my situation. It's not their fault, they have a difficult job. My conclusion is that NOW have zero processes to escalate or deal with anything other than 'switch it off and on again' or 'call Openreach', which is not great if they are fiddling with their network. Likelihood is that anyone finding themselves in the same position (but without OpenWRT) is going to have to get an updated router. It might be that NOW have a current model of router that supports MAP-T...but if not, it may take some time for anyone who can do anything about it to notice.

[-rpnz-]

Sadly there's a bug with OpenWRT where by default it asks for MAP-T but doesn't support it by default, without adding the additional map package.

You should have working IPv6 connectivity, so if you run:

`opkg update`

followed by 

`opkg install map`

This will get your IPv4 connectivity back up and working as well (via MAP-T).     You will have a shared IPv4 address by default, but if you would like to be opted out of IPv4 address sharing, send me a direct message and I can arrange that for you.

[David_Evans]

Thanks, much appreciated - have messaged you. Interested to know about the Openwrt bug - great if you have any more details.

David

[-rpnz-]

No worries.  The OpenWRT bug report can be found here.

[David_Evans]

Ahh, this is as you say an issue with Openwrt, here's the ticket:

https://github.com/openwrt/openwrt/issues/14056

Many thanks,

David

[David_Evans]

Oops - post crossed in the ether.

[David_Evans]

Just to give a public thanks to @-rpnz- for his help and patience in resolving this - very much appreciated.

[someone-else123]

In case anyone else comes across this, they've fixed the bug upstream in odhcp6c (the DHCP client for IPv6 on openwrt) which always tells your ISP that you want to use MAP-T, but some updates to some other places (the map/MAP-T package for one) need to take place before they'll officially release the package.

If you're happy  with a version of odhcp6c which will currently never ask for MAP-T then you can modify the following Dockerfile to build the package for your device (you'll probably need to change the SDK to match your device's architecture).

```

# Because there's a bug in the mainline version of odhcp6c currently in use in openwrt which causes sky to try to force me onto MAP-T (no NATs kthnx!)

# <https://github.com/openwrt/openwrt/issues/14056>

# The bug has been fixed in the main repo but it hasn't been released

# Done with help from <https://github.com/sinancetinkaya/odhcp6c>

FROM debian:12.12

RUN apt-get update && apt-get install -y build-essential clang flex bison g++ gawk \

gcc-multilib g++-multilib gettext git libncurses5-dev libssl-dev \

python3-setuptools rsync swig unzip zlib1g-dev file wget cmake zstd

# Install the lightweight SDK for the appropriate architecture so we can build the relevant package.

RUN wget https://downloads.openwrt.org/releases/24.10.4/targets/mediatek/filogic/openwrt-sdk-24.10.4-mediatek...

RUN tar --zstd -xvf openwrt-sdk-24.10.4-mediatek-filogic_gcc-13.3.0_musl.Linux-x86_64.tar.zst \

&& mv /openwrt-sdk-24.10.4-mediatek-filogic_gcc-13.3.0_musl.Linux-x86_64 /openwrt \

&& rm /openwrt-sdk-24.10.4-mediatek-filogic_gcc-13.3.0_musl.Linux-x86_64.tar.zst

WORKDIR /openwrt

ENV STAGING_DIR=/openwrt/staging_dir

ENV TOOLCHAIN_PATH=$STAGING_DIR/toolchain-aarch64_cortex-a53_gcc-13.3.0_musl

ENV PATH=$TOOLCHAIN_PATH/bin:$PATH

ENV TOOLCHAIN_PREFIX=aarch64-openwrt-linux-

WORKDIR /

RUN git clone https://github.com/sinancetinkaya/odhcp6c.git

WORKDIR /odhcp6c

RUN cmake . -DCMAKE_TOOLCHAIN_FILE=./toolchain-openwrt-armv8.cmake

RUN make -j

# the binary is then available at /odhcp6c/odhcp6c

# Run this once the file is on the router: cp /usr/sbin/odhcp6c /usr/sbin/odhcp6c.old && cp /root/odhcp6c /usr/sbin/

# And then try it out?

```

Just an FYI for anyone who wants IPv4 to work with this configuration: You'll need to set the `client-id`/DNS Option 61 on your ipv4 DHCP config in order to authenticate and get your genuine IPv4 Address. I picked up mine from by tcpdumping the DHCP requests sent out by the router sky sent me.

No idea why Sky decided to suddenly change my connection to make the above necessary and waste a whole load of my time without telling me what was happening, but I guess this is just a symptom of our modern world. 

[someone-else123]

Maybe using the official openwrt repo for odhcp6c is a better idea. It's a shame I can't edit the previous post:

https://github.com/openwrt/odhcp6c.git