866
PowerConnect B-Series FCX Configuration Guide
53-1002266-01
Configuring IP parameters – Layer 2 Switches
26
By allowing multiple subnet DHCP requests to be sent on the same wire, you can reduce the
number of router ports required to support secondary addressing as well as reduce the number of
DHCP servers required, by allowing a server to manage multiple subnet address assignments.
FIGURE 135
DHCP requests in a network without DHCP Assist on the Layer 2 Switch
In a network operating without DHCP Assist, hosts can be assigned IP addresses from the wrong
subnet range because a router with multiple subnets configured on an interface cannot distinguish
among DHCP discovery packets received from different subnets.
For example, in
Figure 135
, a host from each of the four subnets supported on a Layer 2 Switch
requests an IP address from the DHCP server. These requests are sent transparently to the router.
Because the router is unable to determine the origin of each packet by subnet, it assumes the
lowest IP address or the ‘primary address’ is the gateway for all ports on the Layer 2 Switch and
stamps the request with that address.
When the DHCP request is received at the server, it assigns all IP addresses within that range only.
With DHCP Assist enabled on a Layer 2 Switch, correct assignments are made because the Layer 2
Switch provides the stamping service.
Step 3:
DHCP Server gener
a
te
s
IP
a
ddre
ss
e
s
for Ho
s
t
s
1,2,3
a
nd 4.
All IP
a
ddre
ss
a
re
ass
igned
in the 192.95.5.1 r
a
nge.
DHCP req
u
e
s
t
s
for the other
su
b-net
s
were not recognized by
the non-DHCP
ass
i
s
t ro
u
ter c
aus
ing
incorrect
a
ddre
ss
ass
ignment
s
.
DHCP
Server
207.95.7.6
192.95.5.35
192.95.5.5
192.95.5.30
192.95.5.10
Ro
u
ter
L
a
yer 2 Switch
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
H
u
b
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
b-net
s
1, 2, 3
a
nd 4.
Step 2:
Ro
u
ter
assu
me
s
the lowe
s
t
IP
a
ddre
ss
(192.95.5.1) i
s
the
g
a
tew
a
y
a
ddre
ss
.
192.95.5.1
200.95.6.1
202.95.1.1
202.95.5.1
IP addresses configured
on the router interface.
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 ...