consistent value. The MTU size can also be different for various types of traffic sent from one host to the
same endpoint.
Path MTU discovery (PMTD) identifies the path MTU value between the sender and the receiver, and uses
the determined value to transmit packets across the network. PMTD, as described in RFC 1191, denotes
that the default byte size of an IP packet is 576. This packet size is called the maximum transmission unit
(MTU) for IPv4 frames. PMTD operates by containing the do not fragment (DF) bit set in the IP headers of
outgoing packets. When any device along the network path contains an MTU that is smaller than the size
of the packet that it receives, the device drops the packet and sends an Internet Control Message
Protocol (ICMP) Fragmentation Needed (Type 3, Code 4) message with its MTU value to the source or the
sending device. This message enables the source to identify that the transmitted packet size must be
reduced. The packet is retransmitted with a lower size than the previous value. This process is repeated in
an interactive way until the MTU of the transmitted packet is lower or equal to the MTU of the receiving
device for it to obtain the packet without fragmentation. If the ICMP message from the receiving device,
which is sent to the originating device, contains the next-hop MTU, then the sending device lowers the
packet size accordingly and resends the packet. Otherwise, the iterative method is followed until the
packet can traverse without being fragmented.
PMTD is enabled by default on the switches that support this capability. To enable PMTD to function
correctly, you must enter the
ip unreachables
command on a VLAN interface to enable the
generation of ICMP unreachable messages. PMTD is supported on all the layer 3 VLAN interfaces.
Because all of the Layer 3 interfaces are mapped to the VLAN ID of 4095 when VLAN sub-interfaces are
configured on it, it is not possible to configure unique layer 3 MTU values for each of the layer 3
interfaces. If a VLAN interface contains both IPv4 and IPv6 addresses configured on it, both the IPv4 and
IPv6 traffic are applied the same MTU size; you cannot specify different MTU values for IPv4 and IPv6
packets.
Using the Configured Source IP Address in ICMP
Messages
This feature is supported on the S4820T platform.
ICMP error or unreachable messages are now sent with the configured IP address of the source interface
instead of the front-end port IP address as the source IP address. Enable the generation of ICMP
unreachable messages through the
ip unreachable
command in Interface mode. When a ping or
traceroute packet from an endpoint or a device arrives at the null 0 interface configured with a static
route, it is discarded. In such cases, you can configure Internet Control Message Protocol (ICMP)
unreachable messages to be sent to the transmitting device.
Configuring the ICMP Source Interface
You can enable the ICMP error and unreachable messages to contain the configured IP address of the
source device instead of the previous hop's IP address. This configuration helps identify the devices along
the path because the DNS server maps the loopback IP address to the host name, and does not translate
the IP address of every interface of the switch to the host name.
Configure the source to send the configured source interface IP address instead of using its front-end IP
address in the ICMP unreachable messages and in the
traceroute
command output. Use the
ip icmp
source-interface
interface
or the
ipv6 icmp source-interface
interface
commands in
484
IPv4 Routing
Содержание S4820T
Страница 1: ...Dell Configuration Guide for the S4820T System 9 8 0 0 ...
Страница 282: ...Dell 282 Control Plane Policing CoPP ...
Страница 569: ...Figure 62 Inspecting Configuration of LAG 10 on ALPHA Link Aggregation Control Protocol LACP 569 ...
Страница 572: ...Figure 64 Inspecting a LAG Port on BRAVO Using the show interface Command 572 Link Aggregation Control Protocol LACP ...
Страница 573: ...Figure 65 Inspecting LAG 10 Using the show interfaces port channel Command Link Aggregation Control Protocol LACP 573 ...
Страница 617: ...mac address table static multicast mac address vlan vlan id output range interface Microsoft Network Load Balancing 617 ...
Страница 622: ...Figure 81 Configuring Interfaces for MSDP 622 Multicast Source Discovery Protocol MSDP ...
Страница 623: ...Figure 82 Configuring OSPF and BGP for MSDP Multicast Source Discovery Protocol MSDP 623 ...
Страница 624: ...Figure 83 Configuring PIM in Multiple Routing Domains 624 Multicast Source Discovery Protocol MSDP ...
Страница 629: ...Figure 86 MSDP Default Peer Scenario 2 Multicast Source Discovery Protocol MSDP 629 ...
Страница 630: ...Figure 87 MSDP Default Peer Scenario 3 630 Multicast Source Discovery Protocol MSDP ...
Страница 751: ...10 11 5 2 00 00 05 00 02 04 Member Ports Te 1 2 1 PIM Source Specific Mode PIM SSM 751 ...
Страница 905: ...Figure 112 Single and Double Tag First byte TPID Match Service Provider Bridging 905 ...
Страница 979: ...6 Member not present 7 Member not present Stacking 979 ...
Страница 981: ...storm control Storm Control 981 ...
Страница 999: ... Te 1 1 0 INCON Root Rootguard Te 1 2 0 LIS Loopguard Te 1 3 0 EDS Shut Bpduguard Spanning Tree Protocol STP 999 ...
Страница 1103: ...Figure 134 Setup OSPF and Static Routes Virtual Routing and Forwarding VRF 1103 ...