IP networks
NRS II tests your command of IPv4 and IPv6 addressing and forwarding as implemented on Nokia SR OS: how a physical port becomes a router interface, how addresses and subnets are applied, and how packets are resolved and forwarded. Expect questions on subnetting, point-to-point addressing, IPv6 neighbor discovery, MTU handling and basic services such as DHCP and DNS.
Address and interface rules
- A port must be assigned to a router interface; an address is then applied under
config>router>interface. - /31 is valid and preferred on point-to-point links (RFC 3021); /30 is the older alternative.
- Secondary IPv4 addresses let one interface serve multiple subnets.
- IPv6 interfaces normally use /64; /127 is common on point-to-point links. Link-local (fe80::/10) is always present and is used for ND and next-hop resolution.
- ARP resolves IPv4 to MAC; ND does the same for IPv6 and also provides SLAAC and router advertisement.
Worked example - summarization
Sites use 10.20.0.0/24, 10.20.1.0/24, 10.20.2.0/24 and 10.20.3.0/24. The third octet ranges 0–3, i.e. two low-order bits vary, so the summary mask is 24 − 2 = /22. Summary: 10.20.0.0/22. A router receiving this advertisement forwards all four /24s toward the summarizer; if one site is later moved elsewhere, a more specific /24 must be advertised so longest-prefix match wins.
Traps
- Using a /30 where a /31 is intended and wasting two addresses - or, worse, overlapping the two addresses.
- Assuming a /64 is required on point-to-point IPv6 links; it works but wastes space and invites ND scaling issues.
- Forgetting that a packet larger than the egress MTU with DF set triggers ICMP "fragmentation needed"; if that ICMP is filtered, PMTUD black-holes.
- Mixing up ARP cache entries with router interface addresses when troubleshooting.