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Today's Topics:
1. Re: DHCP server configuration does not work for all clients
(Jim Yang)
----------------------------------------------------------------------
Message: 1
Date: Thu, 8 Oct 2020 19:25:15 +0000
From: Jim Yang <z...@cornell.edu>
To: Users of ISC DHCP <dhcp-users@lists.isc.org>
Subject: Re: DHCP server configuration does not work for all clients
Message-ID: <423d0af8-835c-4fa7-85b8-32166a685...@cornell.edu>
Content-Type: text/plain; charset="utf-8"
Hi,
I made some corrections in my initial email. Sorry for the confusion.
My DHCP server software is dhcpd v4.4.2 and running on CentOS 7. The DHCP
Server IP address is 10.2.1.10.
In the example, the client MAC is 74:a7:11:22:33:44 and its IP is 10.1.14.94.
After I added the client MAC to the subclass "mytest" in the dhcpd.conf and
restarted the dhcpd,
I expected the client's next DHCP renew request would not succeed because of
the following statement:
deny members of "mytest" in the pool (range 10.1.1.1 10.1.16.255) definition.
But it did not happen. The client did renewing its address 10.1.14.94 after the
servers restarted.
By comparison, I added a few other clients to the subclass "mytest" in the
dhcpd.conf file and restarted the dhcp servers. Those clients did not renew
their existing IPs in the range 10.1.1.1 10.1.16.255, instead, got their new IP
addresses from the other pool range 10.1.252.1 10.1.255.254. These clients'
behavior is expected.
Is this a DHCP sever software bug or something else?
Thanks for your time.
Related lines in the dhcpd.conf:
shared-network net580 {
option domain-name "test.domain.name";
option domain-name-servers 10.3.1.2,10.3.1.3,10.3.1.4;
subnet 10.1.0.0 netmask 255.255.0.0 {
option routers 10.1.0.1;
}
pool {
failover peer "dhcpnet";
deny dynamic bootp clients;
range 10.1.1.1 10.1.16.255;
deny members of "mytest";
default-lease-time 3600;
max-lease-time 3600;
}
pool {
failover peer "dhcpnet";
deny dynamic bootp clients;
range 10.1.252.1 10.1.255.254;
allow members of "mytest";
default-lease-time 300;
max-lease-time 300;
option domain-name-servers 10.2.1.10, 10.2.1.2;
}
}
subclass "mytest" 1:74:A7:11:22:33:44;
Tcpdump DHCP Packets:
13:25:11.943051 IP (tos 0x0, ttl 62, id 23969, offset 0, flags [none], proto
UDP (17), length 354)
10.1.0.3.bootps > 10.2.1.10.bootps: [udp sum ok] BOOTP/DHCP, Request from
74:a7:11:22:33:44, length 326, xid 0xffc1ae1b, secs 65535, Flags [none] (0x0000)
Gateway-IP 10.1.0.3
Client-Ethernet-Address 74:a7:11:22:33:44
Vendor-rfc1048 Extensions
Magic Cookie 0x65835363
DHCP-Message Option 53, length 1: Request
Requested-IP Option 50, length 4: 10.1.14.94
Server-ID Option 54, length 4: 10.2.1.10
MSZ Option 57, length 2: 1500
Vendor-Class Option 60, length 12: "dhcpcd-5.5.6"
Hostname Option 12, length 16: "amazon-72fdddaaa"
Parameter-Request Option 55, length 10:
Subnet-Mask, Static-Route, Default-Gateway, Domain-Name-Server
Domain-Name, MTU, BR, Lease-Time
RN, RB
Agent-Information Option 82, length 20:
Circuit-ID SubOption 1, length 18: IRB-irb.2043:ae3.0
END Option 255, length 0
13:25:11.943058 IP (tos 0x0, ttl 62, id 39591, offset 0, flags [none], proto
UDP (17), length 355)
10.1.0.2.bootps > 10.2.1.10.bootps: [udp sum ok] BOOTP/DHCP, Request from
74:a7:11:22:33:44, length 327, xid 0xffc1ae1b, secs 65535, Flags [none] (0x0000)
Gateway-IP 10.1.0.2
Client-Ethernet-Address 74:a7:11:22:33:44
Vendor-rfc1048 Extensions
Magic Cookie 0x65835363
DHCP-Message Option 53, length 1: Request
Requested-IP Option 50, length 4: 10.1.14.94
Server-ID Option 54, length 4: 10.2.1.10
MSZ Option 57, length 2: 1500
Vendor-Class Option 60, length 12: "dhcpcd-5.5.6"
Hostname Option 12, length 16: "amazon-72fdddaaa"
Parameter-Request Option 55, length 10:
Subnet-Mask, Static-Route, Default-Gateway, Domain-Name-Server
Domain-Name, MTU, BR, Lease-Time
RN, RB
Agent-Information Option 82, length 21:
Circuit-ID SubOption 1, length 19: IRB-irb.2000:ae00.0
END Option 255, length 0
13:25:11.943779 IP (tos 0x0, ttl 64, id 37878, offset 0, flags [DF], proto UDP
(17), length 365)
10.2.1.10.bootps > 10.1.0.3.bootps: [bad udp cksum 0xc984 -> 0xdcb7!]
BOOTP/DHCP, Reply, length 337, xid 0xffc1ae1b, secs 65535, Flags [none] (0x0000)
Your-IP 10.1.14.94
Gateway-IP 10.1.0.3
Client-Ethernet-Address 74:a7:11:22:33:44
Vendor-rfc1048 Extensions
Magic Cookie 0x65835363
DHCP-Message Option 53, length 1: ACK
Server-ID Option 54, length 4: 10.2.1.10
Lease-Time Option 51, length 4: 3600
Subnet-Mask Option 1, length 4: 255.255.0.0
Default-Gateway Option 3, length 4: 10.1.0.1
Domain-Name-Server Option 6, length 12: 10.3.1.2,10.3.1.3,10.3.1.4
Domain-Name Option 15, length 31: "test.domain.name"
Agent-Information Option 82, length 20:
Circuit-ID SubOption 1, length 18: IRB-irb.2043:ae3.0
END Option 255, length 0
13:25:11.944080 IP (tos 0x0, ttl 64, id 44173, offset 0, flags [DF], proto UDP
(17), length 366)
10.2.1.10.bootps > 10.1.0.2.bootps: [bad udp cksum 0xc984 -> 0xa7b5!]
BOOTP/DHCP, Reply, length 338, xid 0xffc1ae1b, secs 65535, Flags [none] (0x0000)
Your-IP 10.1.14.94
Gateway-IP 10.1.0.2
Client-Ethernet-Address 74:a7:11:22:33:44
Vendor-rfc1048 Extensions
Magic Cookie 0x65835363
DHCP-Message Option 53, length 1: ACK
Server-ID Option 54, length 4: 10.2.1.10
Lease-Time Option 51, length 4: 3600
Subnet-Mask Option 1, length 4: 255.255.0.0
Default-Gateway Option 3, length 4: 10.1.0.1
Domain-Name-Server Option 6, length 12: 10.3.1.2,10.3.1.3,10.3.1.4
Domain-Name Option 15, length 31: "test.domain.name"
Agent-Information Option 82, length 21:
Circuit-ID SubOption 1, length 19: IRB-irb.2000:ae00.0
END Option 255, length 0
Thanks,
Jim Yang
Cornell IT
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