
Chapter 9
| General Security Measures
DHCPv4 Snooping
– 307 –
◆
When DHCP snooping is enabled, the rate limit for the number of DHCP
messages that can be processed by the switch is 100 packets per second. Any
DHCP packets in excess of this limit are dropped.
◆
Filtering rules are implemented as follows:
■
If global DHCP snooping is disabled, all DHCP packets are forwarded.
■
If DHCP snooping is enabled globally, and also enabled on the VLAN where
the DHCP packet is received, all DHCP packets are forwarded for a
trusted
port. If the received packet is a DHCP ACK message, a dynamic DHCP
snooping entry is also added to the binding table.
■
If DHCP snooping is enabled globally, and also enabled on the VLAN where
the DHCP packet is received, but the port is
not trusted
, it is processed as
follows:
■
If the DHCP packet is a reply packet from a DHCP server (including
OFFER, ACK or NAK messages), the packet is dropped.
■
If the DHCP packet is from a client, such as a DECLINE or RELEASE
message, the switch forwards the packet only if the corresponding
entry is found in the binding table.
■
If the DHCP packet is from client, such as a DISCOVER, REQUEST,
INFORM, DECLINE or RELEASE message, the packet is forwarded if MAC
address verification is disabled (as specified by the
command). However, if MAC address verification is
enabled, then the packet will only be forwarded if the client’s hardware
address stored in the DHCP packet is the same as the source MAC
address in the Ethernet header.
■
If the DHCP packet is not a recognizable type, it is dropped.
■
If a DHCP packet from a client passes the filtering criteria above, it will only
be forwarded to trusted ports in the same VLAN.
■
If a DHCP packet is from server is received on a trusted port, it will be
forwarded to both trusted and untrusted ports in the same VLAN.
◆
If DHCP snooping is globally disabled, all dynamic bindings are removed from
the binding table.
◆
Additional considerations when the switch itself is a DHCP client
– The port(s)
through which the switch submits a client request to the DHCP server must be
configured as trusted (using the
command). Note that
the switch will not add a dynamic entry for itself to the binding table when it
receives an ACK message from a DHCP server. Also, when the switch sends out
DHCP client packets for itself, no filtering takes place. However, when the
Содержание ECS4120-28F
Страница 36: ...Contents 36...
Страница 38: ...Figures 38...
Страница 46: ...Section I Getting Started 46...
Страница 70: ...Chapter 1 Initial Switch Configuration Setting the System Clock 70...
Страница 86: ...Chapter 2 Using the Command Line Interface CLI Command Groups 86...
Страница 202: ...Chapter 5 SNMP Commands Additional Trap Commands 202...
Страница 210: ...Chapter 6 Remote Monitoring Commands 210...
Страница 216: ...Chapter 7 Flow Sampling Commands 216...
Страница 278: ...Chapter 8 Authentication Commands PPPoE Intermediate Agent 278...
Страница 360: ...Chapter 9 General Security Measures Port based Traffic Segmentation 360...
Страница 384: ...Chapter 10 Access Control Lists ACL Information 384...
Страница 424: ...Chapter 11 Interface Commands Power Savings 424...
Страница 446: ...Chapter 13 Power over Ethernet Commands 446...
Страница 456: ...Chapter 14 Port Mirroring Commands RSPAN Mirroring Commands 456...
Страница 488: ...Chapter 17 UniDirectional Link Detection Commands 488...
Страница 494: ...Chapter 18 Address Table Commands 494...
Страница 554: ...Chapter 20 ERPS Commands 554...
Страница 620: ...Chapter 22 Class of Service Commands Priority Commands Layer 3 and 4 620...
Страница 638: ...Chapter 23 Quality of Service Commands 638...
Страница 772: ...Chapter 25 LLDP Commands 772...
Страница 814: ...Chapter 26 CFM Commands Delay Measure Operations 814...
Страница 826: ...Chapter 27 OAM Commands 826 1 1 00 12 CF 6A 07 F6 000084 Enabled Disabled Enabled Disabled Console...
Страница 836: ...Chapter 28 Domain Name Service Commands 836...
Страница 848: ...Chapter 29 DHCP Commands DHCP Relay Option 82 848...
Страница 902: ...Section III Appendices 902...
Страница 916: ...Glossary 916...
Страница 926: ...CLI Commands 926...
Страница 937: ......
Страница 938: ...E092017 CS R02...