GoFibre install

I thought I would post this as there is a shortage of information on the GoFibre setup and it might help others. I have just had my installation done today which was somewhat non-standard. I had run 25mm flexible metal conduit from the back of the house just under the soffit to my "computer cupboard" where it comes out into a standard 47mm deep back box. I had put an electrician's fish tape in for easy installation and lent a hand to pull the fibre through with the installer guiding it into the conduit.

Given the pro nature of my setup, the installer was happy to leave me to tidy things up in the cupboard. He did leave an enormous box to go on the wall which is designed to hold the excess fibre coiled up and then hold the ONT. I ditched that and used one of these
wall mount fibre optic junction box with a coupler and 1m patch lead because once I install all the equipment back in the rack access to the ONT would be difficult. I can now go on a rack shelf with my router. GoFibre are currently splicing the SC connector onto the fibre in the house and that complicated the installation as the splicer kept breaking the fibre. The 25mm conduit is to cover me down the line if the fibre breaks and they have moved to a connectorised solution.

Anyway looks like GoFibre is using Nokia kit and supplied an XS-010X-Q ONT along with a Zyxel EX3301-TO router. That didn't last long. They are using PPPoE (what the fascination with PPPoE is in the UK god only knows) and your username and password which are the same, can easily be recovered from the supplied router. I then changed it out for my Edgerouter 6P and everything came up fine.

One thing I was puzzled about is that the MTU on the Zyxel was set to 1480, which seemed on the low side to me and for now I have replicated it on the Edgerouter. Normally you would set it to 1492 on PPPoE if your "modem" only handles standard Ethernet packets. It was set for IPv4/IPv6 dual stack so whether that has anything to do with it I don't know. I will have to play around with that later. For now, it has an IPv4 address which is fine as that's all PlusNet offers which is my previous ISP. Might need to put the Zyxel back in to have a gander at what they are doing. I have no experience with IPv6 as I work at a university which has a class B allocation so even my desktop has a public IP address and PlusNet doesn't do IPv6 either.

I have not taken a phone line from them and I presume that would be provided via the Zyxel as it has a couple of FXS sockets on the back. I am however paying the extra £5 a month for a static IP, I believe otherwise you get CGNAT. One pleasant surprise is that I get 60Mbps upload on the 300Mbps download package. I was expecting it to be 30Mbps which is what their website says, but the installer seemed to think that was normal so I am not going to complain.

In reply to a post by jabuzzard:

One thing I was puzzled about is that the MTU on the Zyxel was set to 1480, which seemed on the low side to me and for now I have replicated it on the Edgerouter. Normally you would set it to 1492 on PPPoE if your "modem" only handles standard Ethernet packets. It was set for IPv4/IPv6 dual stack so whether that has anything to do with it I don't know. I will have to play around with that later. For now, it has an IPv4 address which is fine as that's all PlusNet offers which is my previous ISP. Might need to put the Zyxel back in to have a gander at what they are doing. I have no experience with IPv6 as I work at a university which has a class B allocation so even my desktop has a public IP address and PlusNet doesn't do IPv6 either.

Strictly the MTU of 1500 (or 1492) don't have anything to do with dual stack, and 1480 might be a misunderstanding in the ISP unless some kind of overlay is delivering your connectivity (less common in UK).

The MSS is different between IPv4 and IPv6 but that is normally calculated automatically from the MTU for each protocol,
so MTU-40 for IPv4 and MTU-60 for IPv6.
MSS-clamping is where it might be lowered further for connections initiated your side based on some additional overhead.

In general you leave PMTUD to do its thing as hosts are able to remember different MTUs for different connections as long as the near and far end do not block the ICMP error replies regarding this.

In reply to a post by prlzx:

Strictly the MTU of 1500 (or 1492) don't have anything to do with dual stack, and 1480 might be a misunderstanding in the ISP unless some kind of overlay is delivering your connectivity (less common in UK).

The MSS is different between IPv4 and IPv6 but that is normally calculated automatically from the MTU for each protocol,
so MTU-40 for IPv4 and MTU-60 for IPv6.
MSS-clamping is where it might be lowered further for connections initiated your side based on some additional overhead.

In general you leave PMTUD to do its thing as hosts are able to remember different MTUs for different connections as long as the near and far end do not block the ICMP error replies regarding this.

I have a feeling that the GoFibre are on the crack pipe.

I was using an HG612 in combination with an Edgerouter-X SFP on PlusNet. Many years ago now I needed to set the MTU to 1492 and then set MSS clamping to make it all work. This was because I was under the mistaken impression that the HG612 didn't support baby jumbo frames. However, I found out tonight that the HG612 does indeed support baby jumbo frames if not documented or at least poorly documented.

However, with some experimentation on my Edgerouter 6P (I upgraded prior to the fibre being fitter) I was able to set the MTU to 1508 on the interface connected to the ONT and the MTU in the PPPoE setup to 1500, force a reconnect and was able to ping from the Edgerouter with 1472 byte packets so all is good. It took me a minute to realize that I still had an MSS clamping size of 1452 in the firewall setup when I tried from my workstation and it failed. Then a couple more minutes of fiddling with the Edgerouter before I worked out it would only let me set the MSS clamping option to none standard sizes and you have to remove the setting altogether if you need a standard MSS clamping size

I also plugged the Zxyel back in for a bit to take a look at the IPv6 setup. It would appear IPv6 works. However, despite having decades of IPv4 networking experience (day job is an HPC facility at a UK University) due to having prior to today zero experience with IPv6 (no IPv6 deployed at work because we are IPv4 rich) I am not doing to well getting it working. I have got an IPv6 address onto the Edgerouter and I can ping6 a range of servers on the internet but getting it onto hosts on my network has so far drawn a blank

I also seem to have been assigned a /128 which from my basic understanding of IPv6 is a what the hell.

In reply to a post by jabuzzard:

I also seem to have been assigned a /128 which from my basic understanding of IPv6 is a what the hell.

??? Are you sure? That looks like you would either be constrained to 1 machine on the internet or have to use NAT on IPv6. Not what is intended for IPv6

Or is it just the case that you will be assigned addresses for machines as required?

/128 is commonly seen if you have DHCPv6 but the Router Advertisement (RA) is missing something.
Since DHCPv6 can assign addresses from a pool but not networks or routes.

Client devices will report their address as being part of a /64 subnet when they have an RA for that subnet.
The DNS settings should normally be sent in the RA (RDNSS) and optionally on DHCPv6 also.
(because a DHCP server is an optional thing in IPv6).

Clients should also get a default route (for the internet) if the Router Lifetime in the RA is > 0.
Otherwise it's valid to have self-contained networks without internet access in cases where that is by design.

For EdgeRouter I thought there was a Wizard that would setup DHCPv6-PD on WAN and one LAN
(router as a client requests a network prefix say /56 or /48 delegation from ISP
and then assigns a /64 to one or more LANs from that summary range).

That normally configures the WAN and RA for a chosen LAN.
Then you would be able to back that up and adapt it to your own preferences.

EdgeRouter does still expose more of the settings in the configuration tree than in the main web configuration pages.

I did begin to wonder if it was like the /30's we use for OSPF. I think I need to sit down and actually learn about IPv6 rather than just prodding at it with my limited knowledge. I can see why networks are not keen on deploying IPv6 at work given that being a university we are rich in IPv4 addresses. At one point not so long ago we where handing out public IPv4 addresses to devices on Eduroam, yep your phone got a public IPv4 address!!!

I guess before I spend too much time on it I should check with GoFibre if the IPv6 network assignments they hand out are static because if they are not then they are not very useful anyway. Though I guess I can fiddle with it during working hours and write it off as "professional development"

As for wizards on the Edgerouters I don't have a scooby about those. I know I took a look at the web interface when we got our first pair of Edgerouter 8's over a decade ago now, but as I recall they were set up using the command line. Certainly, the pair of Infinities were set up using the command line as where my Edgeroute X-SFP and 6P.

All the networking at work is all done by command line, in part because all the switches and routers are hooked up to a serial console server which can be accessed out of band remotely. That enables us to fix things up remotely if things go wrong. So being able to configure things with the command line is important, and practice makes perfect. It's the same reason I use vi as an editor a lot of the time. It's the only editor I can rely on to be available when everything goes pear shaped. I just do at home what I do at work because learning the web interface would be something extra

Good job I checked before spending more time on it. Turns out they give a /60 but it is dynamically allocated which is about as useful as a chocolate teapot to me. IMHO if you want a static IPv4 address then there is a good chance you want a static IPv6 allocation too. I guess they are thinking that customers only want a static IPv4 address to get around the limitations of CGNAT not because they actually need a static IPv4 address.

In reply to a post by jabuzzard:

Good job I checked before spending more time on it. Turns out they give a /60 but it is dynamically allocated which is about as useful as a chocolate teapot to me. IMHO if you want a static IPv4 address then there is a good chance you want a static IPv6 allocation too. I guess they are thinking that customers only want a static IPv4 address to get around the limitations of CGNAT not because they actually need a static IPv4 address.

A /60? That's a new one. I've seen /48, /56 and /64 (and even heard of a /72, but really not sure why they'd do that). But never a /60.

I also don't know why ISPs are using dynamic IPv6 prefixes. It surely must be more work to do that, than just give a fixed /64 or /48 and be done with it. Unless it's just a way to make money.. Ohhh, you want a static IPv6. Well that will be £5 a month then.

In reply to a post by agent_r00t:

I also don't know why ISPs are using dynamic IPv6 prefixes. It surely must be more work to do that, than just give a fixed /64 or /48 and be done with it. Unless it's just a way to make money.. Ohhh, you want a static IPv6. Well that will be £5 a month then.

They may be trying to stop people running publically accessible servers.

So while there is nothing technically invalid about a /60 and it is at least a multiple of 4-bits it is not regarded as good practice.
/56 and /48 are considered standard, followed by a single /64 delegation being a sign of an ISP assuming most of their customer base won't know what they are doing with subnets so conservatively only allocating them one LAN subnet unless the customer explicitly requests more when ordering service.

Whereas if driven by a notion of conserving space that can be a sign of IPv4 thinking (scarcity).
A RIPE ISP/LIR that can show a significant % of their space in use for customers can obtain a larger prefix before they "run out".

If it results in packing 15 more customers into adjacent /60s then it goes against guidance about providing an upgrade path that does not require IP renumbering.
A sparse allocation policy that leaves gaps can avoid this (e.g. even if allocating an initial /60 to residential reserve the whole /56, and a customer initially orders with a /56 and is already utilising multiple subnets, maybe reserve a /48, especially if for business).

Edited by prlzx (Sat 17-Aug-24 02:53:33)