Как найти все dhcp сервера в сети

asked Jan 31, 2014 at 16:19

Using the new iproute2 (in my case in Ubuntu 22.04.1 LTS):

$ ip route | grep default

default via 1xx.1xx.xxx.xxx dev gpd0 metric 10 
default via 192.168.xxx.xxx dev wlp0s proto dhcp metric 100 

The DHCP server IP is the one given after the via keyword for each of your specified network interface(s).

ip r | grep default also works.

From the man:

ip route
   Show table routes.

The help:

$ ip route help

$ ip route help
Usage: ip route { list | flush } SELECTOR
       ip route save SELECTOR
       ip route restore
       ip route showdump
       ip route get [ ROUTE_GET_FLAGS ] ADDRESS
                            [ from ADDRESS iif STRING ]
                            [ oif STRING ] [ tos TOS ]
                            [ mark NUMBER ] [ vrf NAME ]
                            [ uid NUMBER ] [ ipproto PROTOCOL ]
                            [ sport NUMBER ] [ dport NUMBER ]
       ip route { add | del | change | append | replace } ROUTE
SELECTOR := [ root PREFIX ] [ match PREFIX ] [ exact PREFIX ]
            [ table TABLE_ID ] [ vrf NAME ] [ proto RTPROTO ]
            [ type TYPE ] [ scope SCOPE ]
ROUTE := NODE_SPEC [ INFO_SPEC ]
NODE_SPEC := [ TYPE ] PREFIX [ tos TOS ]
             [ table TABLE_ID ] [ proto RTPROTO ]
             [ scope SCOPE ] [ metric METRIC ]
             [ ttl-propagate { enabled | disabled } ]
INFO_SPEC := { NH | nhid ID } OPTIONS FLAGS [ nexthop NH ]...
NH := [ encap ENCAPTYPE ENCAPHDR ] [ via [ FAMILY ] ADDRESS ]
      [ dev STRING ] [ weight NUMBER ] NHFLAGS
FAMILY := [ inet | inet6 | mpls | bridge | link ]
OPTIONS := FLAGS [ mtu NUMBER ] [ advmss NUMBER ] [ as [ to ] ADDRESS ]
           [ rtt TIME ] [ rttvar TIME ] [ reordering NUMBER ]
           [ window NUMBER ] [ cwnd NUMBER ] [ initcwnd NUMBER ]
           [ ssthresh NUMBER ] [ realms REALM ] [ src ADDRESS ]
           [ rto_min TIME ] [ hoplimit NUMBER ] [ initrwnd NUMBER ]
           [ features FEATURES ] [ quickack BOOL ] [ congctl NAME ]
           [ pref PREF ] [ expires TIME ] [ fastopen_no_cookie BOOL ]
TYPE := { unicast | local | broadcast | multicast | throw |
          unreachable | prohibit | blackhole | nat }
TABLE_ID := [ local | main | default | all | NUMBER ]
SCOPE := [ host | link | global | NUMBER ]
NHFLAGS := [ onlink | pervasive ]
RTPROTO := [ kernel | boot | static | NUMBER ]
PREF := [ low | medium | high ]
TIME := NUMBER[s|ms]
BOOL := [1|0]
FEATURES := ecn
ENCAPTYPE := [ mpls | ip | ip6 | seg6 | seg6local | rpl | ioam6 ]
ENCAPHDR := [ MPLSLABEL | SEG6HDR | SEG6LOCAL | IOAM6HDR ]
SEG6HDR := [ mode SEGMODE ] segs ADDR1,ADDRi,ADDRn [hmac HMACKEYID] [cleanup]
SEGMODE := [ encap | inline ]
SEG6LOCAL := action ACTION [ OPTIONS ] [ count ]
ACTION := { End | End.X | End.T | End.DX2 | End.DX6 | End.DX4 |
            End.DT6 | End.DT4 | End.DT46 | End.B6 | End.B6.Encaps |
            End.BM | End.S | End.AS | End.AM | End.BPF }
OPTIONS := OPTION [ OPTIONS ]
OPTION := { srh SEG6HDR | nh4 ADDR | nh6 ADDR | iif DEV | oif DEV |
            table TABLEID | vrftable TABLEID | endpoint PROGNAME }
IOAM6HDR := trace prealloc type IOAM6_TRACE_TYPE ns IOAM6_NAMESPACE size IOAM6_TRACE_SIZE
ROUTE_GET_FLAGS := [ fibmatch ]

Current version:

$ ip -V
ip utility, iproute2-5.15.0, libbpf 0.5.0

More:
Web: https://wiki.linuxfoundation.org/networking/iproute2
Git.kernel: https://git.kernel.org/pub/scm/network/iproute2/iproute2.git
Github: https://github.com/shemminger/iproute2

answered Sep 27, 2022 at 19:29

DhcpExplorer – инструмент, позволяющий быстро обнаружить DHCP-сервера в локальной подсети или в сети LAN. Утилита отправляет запрос по локальной подсети для поиска доступных DHCP-серверов, и поэтому будет полезна и удобна для определения серверов, на которых не должно быть в вашей сети, а также проверки ожидаемого отклика известных серверов. Программа обладает доступным для пользователя интерфейсом и простотой пользования.

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