108 lines
4.7 KiB
Markdown
108 lines
4.7 KiB
Markdown
+++
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title = "Fuck U! accept_ra"
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date = "2025-01-11T20:10:37+07:00"
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description = "notice a strange IPv6 on Alpine Linux?, you're cooked. READ MORE"
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slug = "fuck-you-accept-ra"
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#
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# lastmod is optional
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#
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# lastmod = "Timestamp that you edit this blog"
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#
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# description is optional
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#
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# description = "An optional description for SEO. If not provided, an automatically created summary will be used."
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images = ["/images/blog/fuck-you-accept-ra/banner.avif"]
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tags = ["blog","opinion","rant",]
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+++
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Hello internet,
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I decided to write this as a first blog of 2025(HNY🎉) because i spent last fucking week, figuring out what happens with IPv6 on one of my VPS. I don't know if i should call this an **edge**-case or not, because i never have problems like this with any of my vps before, I'll tell you more...
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**TLDR; FUCK YOU accept_ra!**
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## What an actual fuck happens?
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Welp, I got new VPS. and i'm enthusiastic with Alpine Linux lately(I❤️Alpine Linux btw). and what does person when enthusiastic with things especially linux distros, did first? you don't have to guess, fucking bootup Alpine Linux Live CD right away!
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ok, here's when i got confused, i got stuck in `setup-alpine` wtf happens? i already config interfaces why i was able to connect to the internet and now its not? here's what `ip -6 a` looks like:
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```
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inet6 [SUBNET]::216:3eff:fed6:8612/64 scope global dynamic flags 100
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inet6 [SUBNET]::[INTENDED IPv6] scope global
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inet6 [LOCAL SUBNET]::216:3eff:fed6:8612/64 scope link
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```
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notice something strange? yea, the strange IPv6 is on the same subnet as my INTENDED IPv6 and also share the same address if not subnet, with local Subnet.
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B-But! given that the strange IPv6 is dynamics, this's definitely Router Announcement problem, how's this sill happens????! here's mine `/etc/network/interfaces` for inet6:
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```
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iface eth0 inet6 static
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address [SUBNET]::[INTENDED IPv6]
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gateway [SUBNET]::1
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netmask 112
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accept_ra 0
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```
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So, I ticketed the provider regarding issue, but they can't find the cause, cause they can only reproduce this problem only on Alpine Linux😭😭 plus this problem is only reproducible on the REGION that i'm in only!
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Which is also true, I've tested on 3 VM of the same provider. 2 on the same REGION and 1 on the different REGION, and yes, this issue can only reproduce on those 2 VM that's in the same REGION.
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I digged down deeper, and found that to reproduce this issue, you just bring `eth0` interface device up: `ip link set eth0 up`. and it's fucking there:
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```
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inet6 [SUBNET]::216:3eff:fed6:8612/64 scope global dynamic flags 100
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inet6 [LOCAL SUBNET]::216:3eff:fed6:8612/64 scope link
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```
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WTF??? i never face an issue like this before with any distros and on any providers before.
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## And how i fix this mess up?
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I've start reading Docs and Wiki, which i haven't before. And i found this on [Alpine Linux Wiki](https://wiki.alpinelinux.org/wiki/Configure_Networking#IPv6_Static_Address_Configuration).
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Its turn out that `/etc/network/interfaces` doesn't recognize `accept_ra` which i using it on my `/etc/network/interfaces` currently.
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#### TO DISABLE ACCEPTING ROUTER ANNOUNCEMENT:
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```
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iface eth0 inet6 static
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..
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pre-up echo 0 > /proc/sys/net/ipv6/conf/eth0/accept_ra
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```
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([source](https://wiki.alpinelinux.org/wiki/Configure_Networking#IPv6_Static_Address_Configuration))
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this really fix the issue i'm trying to fix for a fucking week!
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okok, what abt Live CD? i mean `setup-interfaces` doesn't support IPv6 yet, but this issue can also happens on Live CD too, how's to fix then?
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#### ON LIVE CD THEN?
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```
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echo 0 > /proc/sys/net/ipv6/conf/eth0/accept_ra
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rc-service networking restart
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```
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if this still doesn't fix, you're **cooked**! still there's a workaround, you can try if you're brave enough :).
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#### WORKAROUNDS
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```
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ip -6 route del default via <Gateway IPv6> dev eth0
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ip -6 route add <your ipv6 ip> dev eth0 metric 66
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ip -6 route add <Gateway IPv6> dev eth0 metric 65
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ip -6 route add default via <Gateway IPv6> dev eth0 src <your ipv6 ip> metric 1
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```
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This workaround required a working IPv6 address.
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This will remove default route(if exist, check with `ip -6 r l`, look for `default via <Gateway IPv6> metric XX` if not, you can simply ignore the first line) and force all route(`::0/0`) to route via `<Gateway IPv6>` with `<your ipv6 ip>`.
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So, the strange ipv6 address will not dissapear but all route will be force to route via your preferred ipv6 ip.
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I know this is dirty but its usable 😄
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{{< rawhtml >}}
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<br>
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<hr>
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{{< /rawhtml >}}
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# This is my fault, anyways, FUCK YOU accept_ra!
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