# The Never-Ending IPv6 Loopback Prefix Saga

DevFeed: [The Never-Ending IPv6 Loopback Prefix Saga](<https://devfeed.tech/articles/the-never-ending-ipv6-loopback-prefix-saga-11423.md>)

Original publisher: [Read original article](<https://blog.ipspace.net/2026/08/ipv6-loopback-saga/>)

Published: 2026-08-17T06:02:00Z

Content type: article

Language: en

Sources: [ipSpace.net blog](<https://devfeed.tech/sources/ipspace-net-blog.md>)

Topics: [Network](<https://devfeed.tech/topics/network.md>), [Hardware](<https://devfeed.tech/topics/hardware.md>), [datacenter](<https://devfeed.tech/topics/datacenter.md>), [BGP](<https://devfeed.tech/topics/bgp.md>)

Tags: [bgp](<https://devfeed.tech/tags/bgp.md>), [datacenter](<https://devfeed.tech/tags/datacenter.md>), [hardware](<https://devfeed.tech/tags/hardware.md>), [ios](<https://devfeed.tech/tags/ios.md>), [ipv6](<https://devfeed.tech/tags/ipv6.md>), [is-is](<https://devfeed.tech/tags/is-is.md>), [netlab](<https://devfeed.tech/tags/netlab.md>), [network](<https://devfeed.tech/tags/network.md>), [ospf](<https://devfeed.tech/tags/ospf.md>), [vxlan](<https://devfeed.tech/tags/vxlan.md>)

## AI overview

The article examines the IPv6 loopback-prefix problem in high-speed routers and data-center switches. OSPFv3 requires loopbacks to be advertised as /128s, which can increase forwarding hardware demands when /64 addressing is preferred. It compares vendor behaviors and suggests IS-IS or BGP as possible alternatives.

## Source excerpt

Remember the sage advice to simplify your life and use the IPv6 /64 prefixes everywhere? Not only does it make your life simpler (and wastes immesuarably less address space than the crazy "let's assign /64 to every device" stupidity), it also reduces the hardware requirements in your high-speed routers layer-3 switches. You see, doing lookups on 64 bits uses half the silicon it takes to do lookups on 128 bits. Alas, some people never got the memo. OSPFv3 standard clearly states in one of the bullets in section 4.4.3.9 that the loopback prefixes should always be advertised as /128s regardless of what's configured on the interface. Read more ...