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ARP: Difference between revisions
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* "[http://www.cs.clemson.edu/~westall/853/notes/arpstate.pdf The ARP State Machine]" James Westall's CpSc 853 "[http://www.cs.clemson.edu/~westall/853/ Protocol Implementation]" class notes | * "[http://www.cs.clemson.edu/~westall/853/notes/arpstate.pdf The ARP State Machine]" James Westall's CpSc 853 "[http://www.cs.clemson.edu/~westall/853/ Protocol Implementation]" class notes | ||
* "[http://linux-ip.net/html/ether-arp.html 2.1 Address Resolution Protocol (ARP)]" Martin Brown's "[http://linux-ip.net/html/index.html Guide to IP Layer Network Administration with Linux]" | * "[http://linux-ip.net/html/ether-arp.html 2.1 Address Resolution Protocol (ARP)]" Martin Brown's "[http://linux-ip.net/html/index.html Guide to IP Layer Network Administration with Linux]" | ||
[[CATEGORY: Networking]] | |||
Revision as of 09:19, 19 July 2011
Linux ARP states
These are encoded in the ndm_state bitmask of a RTM_NEWNEIGH/RTM_GETNEIGH netlink message (valid ndm_flags values include NTF_PROXY for proxy ARP entries and NTF_ROUTER for IPv6 routers).
| state | meaning | transitions |
|---|---|---|
| permanent | never undergoes verification or expiry | none (manually configured) |
| noarp | normal expiration, never verified
"A device with no destination cache" |
use resets use counter |
| reachable | normal expiration | use resets timer |
| stale | still usable, needs verification | use resets timer and returns to reachable
timer changes state to delay |
| delay | schedule ARP request, needs verification | use resets timer and returns to reachable
timer changes state to probe, issuing ARP request |
| probe | need ARP reply for verification (reprobing) | use resets timer and returns to reachable
timer reissues ARP requests or moves to failed |
| incomplete (new entry) | need ARP reply for first use | use resets timer and returns to reachable
timer reissues ARP requests or moves to failed |
| failed | no response received / invalid cache entry | timer governs reissuing of ARP requests
use resets timer and moves to reachable |
See Also
- Linux's rtnetlink(7) man page
- "The ARP State Machine" James Westall's CpSc 853 "Protocol Implementation" class notes
- "2.1 Address Resolution Protocol (ARP)" Martin Brown's "Guide to IP Layer Network Administration with Linux"
