ARP and IPv6 Neighbour Discovery
ARP and IPv6 Neighbour Discovery resolve next-hop addresses into link-layer destinations. They sit below routing and make packet forwarding inspectable.
Support level
Section titled “Support level”| Area | Level | Notes |
|---|---|---|
| ARP | Supported | Request/reply, cache insertion, retry/failure behaviour. |
| IPv6 ND | Supported | Neighbour solicitation/advertisement and neighbour cache. |
| SLAAC | Behaviour model | Router-advertisement-driven address generation solver. |
| Duplicate address detection | Not modelled | Not a current support claim. |
Standards coverage
Section titled “Standards coverage”| Standard | Coverage | Notes |
|---|---|---|
| RFC 826 | Behaviour model | ARP request/reply and cache semantics. |
| RFC 4861 | Behaviour model | IPv6 neighbour solicitation/advertisement. |
| RFC 4862 | Behaviour model | SLAAC address configuration concepts. |
Feature matrix
Section titled “Feature matrix”| Feature | Status | Notes |
|---|---|---|
| ARP cache | Supported | Learns IPv4-to-MAC mappings. |
| ARP retry | Supported | Unresolved next-hop produces deterministic failure. |
| Static ARP | Partial | Supported where parsed. |
| ND cache | Supported | Learns IPv6-to-MAC mappings. |
| SLAAC | Behaviour model | Generates addresses from prefixes where configured. |
| Router advertisement | Partial | Solver-level, not full packet stream. |
Vendor command matrix
Section titled “Vendor command matrix”| Command | IOS-style | Junos-style | VyOS-style | Notes |
|---|---|---|---|---|
show arp | Supported | Partial | Partial | IPv4 cache. |
show ipv6 neighbors | Supported | Partial | Partial | IPv6 ND cache. |
ipv6 address autoconfig | Supported | n/a | Partial | SLAAC intent. |
Behaviour notes
Section titled “Behaviour notes”The neighbour cache is part of forwarding state. If a next hop cannot be resolved, the packet path fails in a way diagnostics can show.
Examples
Section titled “Examples”Canonical example
show arpshow ipv6 neighborsping 10.0.12.2show arpVendor styles
IOS-style
arp 10.0.12.2 0011.2233.4455 arpaipv6 address autoconfigshow arpshow ipv6 neighborsJunos-style
set interfaces ge-0/0/0 unit 0 family inet address 10.0.12.1/30show arp no-resolveshow ipv6 neighborsVyOS-style
set interfaces ethernet eth0 address 10.0.12.1/30run show arprun show ipv6 neighborsKnown limits
Section titled “Known limits”Proxy ARP, DAD, SEND, every RA option, and vendor-specific cache ageing details are not fully modelled.