PowerConnect B-Series FCX Configuration Guide
867
53-1002266-01
Configuring IP parameters – Layer 2 Switches
26
How DHCP Assist works
Upon initiation of a DHCP session, the client sends out a DHCP discovery packet for an address
from the DHCP server as seen in
Figure 136
. When the DHCP discovery packet is received at a
Layer 2 Switch with the DHCP Assist feature enabled, the gateway address configured on the
receiving interface is inserted into the packet. This address insertion is also referred to as
stamping.
FIGURE 136
DHCP requests in a network with DHCP Assist operating on a PowerConnect Switch
When the stamped DHCP discovery packet is then received at the router, it is forwarded to the
DHCP server. The DHCP server then extracts the gateway address from each request and assigns
an available IP address within the corresponding IP subnet (
Figure 137
). The IP address is then
forwarded back to the workstation that originated the request.
NOTE
When DHCP Assist is enabled on any port, Layer 2 broadcast packets are forwarded by the CPU.
Unknown unicast and multicast packets are still forwarded in hardware, although selective packets
such as IGMP, are sent to the CPU for analysis. When DHCP Assist is not enabled, Layer 2 broadcast
packets are forwarded in hardware.
DHCP
Server
H
u
b
207.95.7.6
Ro
u
ter
Ho
s
t 1
Ho
s
t 2
Ho
s
t 3
Ho
s
t 4
192.95.5.x
S
u
bnet 1
200.95.6.x
S
u
bnet 2
202.95.1.x
S
u
bnet 3
202.95.5.x
S
u
bnet 4
Interf
a
ce 2
Interf
a
ce 14
Interf
a
ce 8
Step 1:
DHCP IP
a
ddre
ss
req
u
e
s
t
s
for Ho
s
t
s
1, 2, 3
a
nd 4 in
S
u
bnet
s
1, 2, 3
a
nd 4.
Gateway addresses:
192.95.5.1
200.95.6.1
202.95.1.1
202.95.5.1
Step 2:
Switch
s
t
a
mp
s
e
a
ch DHCP req
u
e
s
t
with the g
a
tew
a
y
a
ddre
ss
of the
corre
s
ponding
su
bnet of the
receiving port.
Step 3:
Ro
u
ter forw
a
rd
s
the DHCP req
u
e
s
t to the
s
erver witho
u
t to
u
ching the g
a
tew
a
y
a
ddre
ss
in
s
erted in the p
a
cket by the
s
witch.
L
a
yer 2 Switch
Содержание PowerConnect B-FCXs
Страница 1: ...53 1002266 01 18 March 2011 PowerConnect B Series FCX Configuration Guide ...
Страница 136: ...94 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Viewing information about software licenses 4 ...
Страница 228: ...186 PowerConnect B Series FCX Configuration Guide 53 1002266 01 PowerConnect B Series FCX hitless stacking 5 ...
Страница 229: ...PowerConnect B Series FCX Configuration Guide 187 53 1002266 01 PowerConnect B Series FCX hitless stacking 5 ...
Страница 230: ...188 PowerConnect B Series FCX Configuration Guide 53 1002266 01 PowerConnect B Series FCX hitless stacking 5 ...
Страница 248: ...206 PowerConnect B Series FCX Configuration Guide 53 1002266 01 IPv6 management commands 7 ...
Страница 346: ...304 PowerConnect B Series FCX Configuration Guide 53 1002266 01 802 1s Multiple Spanning Tree Protocol 8 ...
Страница 374: ...332 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Jumbo frame support 9 ...
Страница 424: ...382 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Virtual Switch Redundancy Protocol VSRP 10 ...
Страница 568: ...526 PowerConnect B Series FCX Configuration Guide 53 1002266 01 CLI examples 14 ...
Страница 588: ...546 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Sample application 15 ...
Страница 674: ...632 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Enabling or disabling layer 2 switching 19 ...
Страница 684: ...642 PowerConnect B Series FCX Configuration Guide 53 1002266 01 VLAN based mirroring 20 ...
Страница 724: ...682 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Reading CDP packets 23 ...
Страница 768: ...726 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Clearing cached LLDP neighbor information 24 ...
Страница 930: ...888 PowerConnect B Series FCX Configuration Guide 53 1002266 01 26 ...
Страница 948: ...906 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Configuring MLD snooping 27 ...
Страница 962: ...920 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Displaying CPU utilization statistics 28 ...
Страница 1022: ...980 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Displaying OSPF information 29 ...
Страница 1142: ...1100 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Clearing diagnostic buffers 30 ...
Страница 1258: ...1216 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Using Secure copy with SSH2 33 ...
Страница 1314: ...1272 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Displaying port security information 35 ...
Страница 1348: ...1306 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Example configurations 36 ...
Страница 1406: ...1364 PowerConnect B Series FCX Configuration Guide 53 1002266 01 IP source guard 39 ...
Страница 1422: ...1380 PowerConnect B Series FCX Configuration Guide 53 1002266 01 SNMP v3 Configuration examples 40 ...