76 lines
2 KiB
Markdown
76 lines
2 KiB
Markdown
title: Announcing IPv6 networks without becoming the default router
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---
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pub_date: 2020-01-31
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---
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author: ungleich network team
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---
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twitter_handle: ungleich
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---
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_hidden: no
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---
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_discoverable: yes
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---
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abstract:
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You can also announce prefixes without becoming the default router
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---
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body:
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## TL;DR
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Use **AdvDefaultLifetime 0** in your radvd.conf if you don't want the
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router to become a default router.
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## Background
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Sometimes you have multiple routers in a network and you don't want a
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router to become the default router for clients, but it should still
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announce an IPv6 prefix.
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## radvd
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Luckily radvd supports an option to notify the clients of this. From the manpage of radvd.conf(5):
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```
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AdvDefaultLifetime seconds
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The lifetime associated with the default router in units of seconds. The
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maximum value corresponds to 18.2 hours. A lifetime of 0 indicates that
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the router is not a default router and should not appear on the default
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router list. The router lifetime applies only to the router's usefulness
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as a default router; it does not apply to information contained in other
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message fields or options. Options that need time limits for their infor‐
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mation include their own lifetime fields.
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Must be either zero or between MaxRtrAdvInterval and 9000 seconds.
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Default: 3 * MaxRtrAdvInterval (Minimum 1 second).
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```
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## Sample configuration
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A configuration from one of our test sites looks as follows:
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```
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interface eth0
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{
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AdvSendAdvert on;
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MinRtrAdvInterval 3;
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MaxRtrAdvInterval 5;
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AdvDefaultLifetime 0;
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prefix 2a0a:e5c1:111:10c::/64 { };
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};
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```
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Client in this test network assign themselves an additional IPv6
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address from this prefix.
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## Note
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While clients won't select this router as the default router, they
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might still choose to use an IPv6 address from this prefix as their
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**source address**. More details about it can be found in the
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[RFC 6724](https://tools.ietf.org/html/rfc6724).
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