O sistema inicia o relógio no momento em que este também inicia e mantém o registo da data/hora.
O relógio do sistema pode ser atualizado das seguintes formas:
- NTP
- Simple Network Time Protocol (SNTP)
- Virtual Integrated Network Service (VINES) Time Service
- Manual configuration
O NTP permitem garantir a sincronização da data/hora entre os vários elementos, este pode ser configurado nos seguintes modos:
- Client/Server
- Symmetric Active/Passive – Grupo de peers low stratum operam como backups uns dos outros. Cada peer usa as suas referencias primarias e em caso de falha usa os peers, esta operação e descrita como push-pull. Um peer é configurado em modo Symmetric Active usando o comando peer. O outro peer também deve ser configurado da mesma forma.
Nota: Se o outro peer não for configurado com o comando peer, a associacao e feita em Symmetric Passive quando é recebida uma mensagem Symmetric Active. - Broadcast
Exemplo:
Ligações:
R1——-s2/1-R2-f0/1———-f0/0-R3
Autenticar o NTP entre o R1/R3
O R1 deve estar em Symmetric Active mode
O R3 recebe o NTP via broadcast
R1(config)#
ntp authentication-key 1 md5 CCIE
ntp authenticate
ntp trusted-key 1
ntp server 192.168.2.2
ntp peer 192.168.2.2
R2(config)#
ntp authentication-key 1 md5 CCIE
ntp authenticate
ntp trusted-key 1
ntp master 2
R3(config)#
int f0/1
ntp broadcast client
R2#sh ntp associations
address ref clock st when poll reach delay offset disp
*~127.127.7.1 .LOCL. 1 5 64 377 0.0 0.00 0.0
* master (synced), # master (unsynced), + selected, – candidate, ~ configured
R2#sh ntp status
Clock is synchronized, stratum 2, reference is 127.127.7.1
nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**24
reference time is D62E1DCD.301D493F (15:48:29.187 UTC Wed Nov 13 2013)
clock offset is 0.0000 msec, root delay is 0.00 msec
root dispersion is 0.02 msec, peer dispersion is 0.02 msec
R1#sh ntp associations de
192.168.2.2 configured, our_master, sane, valid, stratum 2
ref ID 127.127.7.1, time D62E1E4D.301CB65E (15:50:37.187 UTC Wed Nov 13 2013)
our mode active, peer mode passive, our poll intvl 64, peer poll intvl 64
root delay 0.00 msec, root disp 0.03, reach 377, sync dist 25.284
delay 12.12 msec, offset 6.2250 msec, dispersion 19.20
precision 2**24, version 3
org time D62E1E63.80060ECC (15:50:59.500 UTC Wed Nov 13 2013)
rcv time D62E1E63.7FCF0483 (15:50:59.499 UTC Wed Nov 13 2013)
xmt time D62E1E63.747ED2BE (15:50:59.455 UTC Wed Nov 13 2013)
filtdelay = 44.14 19.94 47.94 12.12 39.92 40.07 27.91 36.16
filtoffset = 22.92 -16.03 3.07 6.23 11.91 -4.44 -2.76 0.59
filterror = 0.02 0.99 1.97 2.94 3.92 4.90 5.87 6.85
R3#sh ntp associations
address ref clock st when poll reach delay offset disp
* 192.168.20.2 127.127.7.1 2 18 64 376 16.1 13.55 15.9
* master (synced), # master (unsynced), + selected, – candidate, ~ configured
R3#sh ntp ass detail
192.168.20.2 dynamic, our_master, sane, valid, stratum 2
ref ID 127.127.7.1, time D62E1E8D.301D95DD (15:51:41.187 UTC Wed Nov 13 2013)
our mode bdcast client, peer mode bdcast, our poll intvl 64, peer poll intvl 64
root delay 0.00 msec, root disp 0.03, reach 376, sync dist 24.002
delay 16.07 msec, offset 13.5468 msec, dispersion 15.95
precision 2**24, version 3
org time D62E1E9C.301B1A0A (15:51:56.187 UTC Wed Nov 13 2013)
rcv time D62E1E9C.2CA64C21 (15:51:56.174 UTC Wed Nov 13 2013)
xmt time 00000000.00000000 (00:00:00.000 UTC Mon Jan 1 1900)
filtdelay = 16.07 16.07 16.07 16.07 16.07 16.07 16.07 16.07
filtoffset = 13.55 1.73 25.91 -16.53 -5.48 -6.40 1.73 -12.14
filterror = 0.99 1.97 2.94 3.92 4.90 5.87 6.85 7.83