Extended Ping (eping)

Network operators use ping to determine whether a remote interface is alive. Ping sends an ICMP Echo message to the interface being probed and waits for an ICMP Echo Reply. If ping receives the expected ICMP Echo Reply, it reports that interface is alive. In order for the Echo message to reach the probed interface, the probed interface must be addressed appropriately. IP addresses are scoped as follows: Global Private Link-local Global addresses are the most widely scoped. A globally addressed interface can be reached from any node on the Internet. By contrast, link-local addresses are the least widely scoped. An interface whose only address is link-local can be reached from on-link interfaces only. Network operators seek to decrease their dependence on widely-scoped interface addressing. For example: The operator of an IPv4 network currently assigns global addresses to all interfaces. In order to conserve scarce IPv4 address space, this operator seeks to renumber selected interfaces with private addresses. The operator of an IPv4 network currently assigns private addresses to all interfaces. In order to achieve operational efficiencies, this operator seeks to leave selected interfaces unnumbered. The operator of an IPv6 network currently assigns global addresses to all interfaces. In order to achieve operational efficiencies, this operator seeks to allow selected interfaces to be automatically configured with link-local addresses. When a network operator renumbers an interface, replacing a more widely-scoped address with a less widely-scope address, the operator also reduces the number of nodes from which ping can probe the interface. Furthermore, when a network operator removes all addresses from an interface, leaving it unnumbered, the operator makes that interface totally inaccessible to ping. Therefore, many network operators who rely on ping remain dependant upon widely-scoped interface addressing. This document describes a new diagnostic tool called Extended Ping (eping). Network operators use eping to determine whether a remote interface is active. In this respect, eping is similar to ping. Eping differs from ping in that it does not require reachability between the probing node and the probed interface. Or, said another way, eping does not require reachability between the node upon which it executes and the interface whose status is being queried. Eping relies on two new ICMP messages, called Extended Echo and Extended Echo Reply. The Extended Echo message makes a semantic distinction between the destination interface and the probed interface. The destination interface is the interface to which the Extended Echo message is delivered. It must be reachable from the probing node. The probed interface is the interface whose status is being queried. It does not need to be reachable from the probing node. However, the destination and probed interfaces must be local to one another (i.e., the same node must support both interfaces). Because the Extended Echo message makes a distinction between the destination and probed interfaces, eping can probe every interface on a node if it can reach any node on the node. In many cases, this allows network operators to decrease their dependence on widely-scoped interface addressing. This document is divided into sections, with describing the Extended Echo message and describing the Extended Echo Reply message. describes how the probed node processes the Extended Echo message and describes the eping application.

The ICMP Extended Echo message is applicable to both ICMPv4 and ICMPv6. Like any ICMP message, the ICMP Extended Echo message is encapsulated in an IP header. The ICMPv4 version of the Extended Echo message is encapsulated in an IPv4 header, while the ICMPv6 version is encapsulated in an IPv6 header. depicts the ICMP Extended Echo message.

IP Source Address: Identifies an interface on the probing node. IP Destination Address: Identifies the destination interface (i.e., the interface to which this message will be delivered). Type: Extended Echo (TBD. Value to be assigned by IANA.) Code: 0 Checksum: For ICMPv4, see RFC 792. For ICMPv6, see RFC 4443. Identifier: An identifier to aid in matching Extended Echo Replies to this Extended Echo Request. May be zero. Sequence Number: A sequence number to aid in matching Extended Echo Replies to this Extended Echo Request. May be zero. If the destination interface is different from the probed interface, the Extended Echo message MUST include ICMP Extensions. ICMP Extensions MUST include the ICMP Extension Structure Header and the Interface Identification Object. If the Extended Echo message does not include the Interface Identification Object, the destination and probed interfaces are understood to be the same.

The Interface Identification Object identifies the probed interface. It includes an ICMP Object Header (RFC 4884) and at least one sub-TLV. The ICMP Object Header contains Class-Num and C-Type fields. The Class-Num field MUST be set to Interface Identification Class (value to be assigned by IANA). The C-Type indicates how the probed interface is identified. The C-Type value MUST be one of the following: By Address (value to be assigned by IANA) By ifName (value to be assigned by IANA) By ifIndex (value to be assigned by IANA) See for a definition of the IfName and IfIndex. If C-type equals "By Address", the Identification Object payload MUST be an Interface IP Address Sub-Object. If C-type equals "By ifName", the Identification Object payload MUST be an Interface IP Name Sub-Object. Both of these are defined in . If C-type equals "By ifIndex, the Identification Object payload MUST be a 32-bit ifIndex. If the probed interface is identified by address, its address family does not need to be the same as that of the destination address. For example, the probed interface can be identified by its Ethernet address while the destination address is identified by an IPv4 address. By default, implementations SHOULD NOT support probing by ifName. See for details.

The ICMP Extended Echo Reply message is applicable to both ICMPv4 and ICMPv6. Like any ICMP message, the ICMP Extended Echo Reply message is encapsulated in an IP header. The ICMPv4 version of the Extended Echo Reply message is encapsulated in an IPv4 header, while the ICMPv6 version is encapsulated in an IPv6 header. depicts the ICMP Extended Echo Reply message.

IP source address: Identifies the interface to which the corresponding ICMP Extended Echo message was sent IP destination address: Identifies the interface from which the corresponding ICMP Extended Echo message was sent Type: Extended Echo Reply (TBD. Value to be assigned by IANA.) Code: Indicates operational status of probed interface. Defined values are: Inactive (value to be assigned by IANA) Active (value to be assigned by IANA) Interface_does_not_exist (value to be assigned by IANA) Query_not_supported (value to be assigned by IANA) Checksum: For ICMPv4, see RFC 792. For ICMPv6, see RFC 4443. Identifier: An identifier to aid in matching Extended Echo Replies to this Extended Echo Request. May be zero. Sequence Number: A sequence number to aid in matching Extended Echo Replies to this Extended Echo Request. May be zero. ICMP Extensions: ICMP Extensions are optional. Currently, no extensions are specified for the ICMP Extended Echo Reply message. However, ICMP Extensions may be defined in the future to carry additional OAM information.

When a node receives an ICMPv4 Extended Echo, it MUST format an ICMP Extended Echo Reply as follows: Don't Fragment flag (DF) is 1 More Fragments flag is 0 Fragment Offset is 0 TTL is 255 Protocol is ICMP When a node receives an ICMPv6 Extended Echo, it MUST format an ICMPv6 Extended Echo Reply as follows: Hop Limit is 255 Next Header is ICMPv6 Flow Label is 0 In either case, the responding node MUST: Copy the source address from the Extended Echo message to the destination address of the Extended Echo Reply Copy the destination address from the Extended Echo message to the source address of the Extended Echo Reply Set the DiffServ codepoint to CS0 Set the ICMP Type to Extended Echo Reply Copy the Identifier from the Extended Echo message to the Extended Echo Reply Copy the sequence number from the Extended Echo message to the Extended Echo Reply Set the code appropriately Append ICMP Extensions as required Set the checksum appropriately The following rules govern how the Code should be set: If the query type is not supported, set the Code to Query_not_supported Otherwise, if the interface does not exist, set the Code to Interface_does_not_exist Otherwise, if the destination interface is in one security domain and the probed interface is in another security domain, set the Code to Interface_does_not_exist. Virtual Private Networks are examples of security domains. Otherwise, if the probed inactive, set the Code to Inactive Otherwise, set the code to Active

The eping application accepts input parameters, sets a counter and enters a loop to be exited when the counter is equal to zero. On each iteration of the loop, eping emits an ICMP Extended Echo, decrements the counter, sets a timer, waits for the timer to expire. If an expected ICMP Extended Echo Reply arrives while eping is waiting for the timer to expire, eping relays information returned by that message to its user. However, on each iteration of the loop, eping waits for the timer to expire, regardless of whether an Extended Echo Reply message arrives. Eping accepts the following parameters: Count Wait Source Interface Address Hop Count Destination Interface Address Probed Interface Identifier Count is a positive integer whose default value is 3. Count determines the number of times that eping iterates through the above-mentioned loop. Wait is a positive integer whose minimum and default values are 1. Wait determines the duration of the above mentioned timer, measured in seconds. Source Interface Address specifies the source address of ICMP Extended Echo. The destination Interface Address identifies the interface to which the ICMP Extended Echo message is sent. It can be an IPv4 address or an IPv6 address. If it is an IPv4 address, eping emits an ICMPv4 message. If it is an IPv6 address, eping emits an ICMPv6 message. The probed interface is the interface whose status is being queried. If the probed interface identifier is not specified, the destination and probed interfaces are understood to be identical. If the probed interface identifier is specified, it can be: an interface name an interface description an address from any address family (e.g., IPv4, IPv6, MAC) an ifIndex The probed interface identifier can have any scope. For example, the probed interface identifier can be: an IPv6 address, whose scope is global an IPv6 address, whose scope is link-local an interface name, whose scope is node-local an interface description, whose scope is node-local an ifIndex, whose scope is node-local If the probed interface identifier is an address, it does not need to be of the same address family as the destination interface address. For example, eping accepts an IPv4 destination interface address and an IPv6 probed interface identifier.

This document requests the following actions from IANA: Add an entry to the "ICMP Type Number" registry, representing the Extended Echo. This entry has one code (0). Add an entry to the "ICMP Type Number" registry, representing the Extended Echo Reply. This entry has the following codes: Inactive, Active, Interface_does_not_exist, and Query_not_supported. Add an entry to the "ICMPv6 Type Number" registry, representing the Extended Echo. This entry has the following codes: Inactive, Active, Interface_does_not_exist, and Query_not_supported. Add an entry to the "ICMPv6 Type Number" registry, representing the Extended Echo Reply. This entry has one code (0). Add an entry to the "ICMP Extension Object Classes and sub-classes" registry, representing the Interface Identification Class. This Class includes the sub-classes "By Address", "By Name" , and "By ifIndex". Note to RFC Editor: this section may be removed on publication as an RFC.

Many implementations encode the following information in an ifName: Interface type (e.g.., Gigabit Ethernet, SONET, T1) Location on chassis (i.e., slot identifier) Location on line card (i.e., port identifier) Location on port (i.e., logical port identifier) While an operator may have a requirement to probe ports using eping, that operator may not want to expose the above mentioned information. Therefore, by default, implementations SHOULD NOT support probing by ifName. However, probing by ifName can be enabled through configuration.

TBD