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Network Working Group J. Postel
Request for Comments: 925 ISI
October 1984
Multi-LAN address analysis
(RFC925 - MULTI-LAN ADDRESS RESOLUTION)
Memorandum state
This memo is triggered by Jeffery Mogul triggered the RFC917 of "Internet Internet". In that preparation
Incitted, Mogul created a "explicit subnet" application case in a multi-LAN environment. In this memorandum,
I strive to build a "transparent subnet" case. This RFC has established a conditions submitted by the ARP network organization.
Discuss and request discussions and submit their opinions to further improve. The issuance of this memorandum is unconstrained.
table of Contents
Introduction 1
Introduction 1
Summary 6
Gross 6
Reference: 8
Introduction
Problems with a set of local area networks (LANs) have been widely concerned and interest. in
The local area network in the same place gives an intercounted network number, which is not appropriate. Satisfactory
The practice is that the details of each local domain network in each local area network are hidden in the location of people, gateways and external hosts. facing
The problem is what it is best, and even what I do. A suggestion is to use "Explicit subnet [1]". Explicit subfang
The case is a mechanism for managing multiple networks to manage the management of local area networks in a network.
One of the questions on topics. Please note that I highly recommend another method: use a multi-LAN address resolution association
"Transparent Subnet" supported by the extension.
Insteit
Quickly review the Address Resolution Protocol (ARP). Every host on the broadcast local area is not only known to its bureau
Domain Network Physical Address (HA) also knows its Internet Address (IA). When the host A gets the Host B IA
When sending a datagram to him, host A must know the HA corresponding to host B. In order to achieve this
A purpose, ARP package A generate an ARP package, which contains its own IA and HA addresses, and target hosts.
(Host B) IA. Host A broadcast this ARP package. Hosting this ARP package checks this package to determine
Whether they are looking for a host. If so, they (actually only host b) sends an address to issue a request
The response of the HA address required for host a). Now, host A has achieved destination (host
B) all IA, HA address. For future use, host A add this message to its cache.
Note that ARP is actually more summarized than this brief overview. The point of view of this memo is to extend the ARP so that
It works in a local area network interconnection environment.
In order to understand how he is working, we truly have a "magic box", he is like a usual host.
Connect to two or more LANs.
The behavior of each host should be strictly consistent with the behavior in the basic ARP. When any host broadcasts an ARP request, the box reads it (like all hosts on the local area),
The box checks its cache, saves the IA: HA address mapping of each local area network in the cache, and then determines if it is
The one is looking for (yes, I will reply).
Situation 1: If this host mapping is found in the cache corresponding to the request, the box is found.
Not answer.
Case 2: If this host mapping is found in the cache corresponding to the non-issued LAN, the box
The child issued an answer and gives him his own HA address in the request. Box as a destination host
One agent.
Situation 3: If you can't find that map in any cache, the box must try to find this address, then
The situation is made to react like the case.
In the case of 3, the box had to perform some magic:
The box keeps a searcher search table. Each table item contains the HA address of the hosting host and the original request.
The source address of the host and the interface to which this ARP are received. This search list is checked when the situation 3 occurs. If
The search host has been included in this search list; otherwise, the table is spread.
In order to spread this search list, write a table entry on this search list, and then organize and in addition to receiving
This ARP package is issued on all interfaces outside the interface of the "ARP" package that causes the search. If you receive one should
A, the information will be entered into the corresponding cache, and the corresponding table is deleted in the search list, then the situation is 1 or
The situation 2 will give the "ARP that causing the search" an answer.
If you don't receive a response, stop and don't make anything - no answer to that "trigger" host
(The entry is still left in the search list).
In order to stop search, stop and don't make anything - did not answer the "trigger" host (table
Item still stay in the search list).
The entries in the cache and search list are likely to time out
.
For each ARP request received, the box must also put the IA: HA address mapping of the sender into the connection.
Receive it in the cache of its local area network.
Multi-LAN address analysis
This plan is used or ARP, the new component is just a "magic box" ("Based on ARP bridge"), it will arp
The request is relay to the neighboring LAN to act as a proxy to relate the datagram to the host on other local area.
detail
The behavior of the host should be strictly consistent with the behavior in the basic ARP.
The local area network is connected by "Magic Box" (some icons to the LAN connection with two or more LANs)
Computer). The box executes the program.
Each box holds a list for each local area network it is connected. because
For the table item back time, the entry should be the recent cache. These entries are all local area networks
IA: HA address pair.
When an ARP request is broadcast, the box reads it (such as all the LAN on the local area.
The machine is as follows). In addition, you have to check to see if he is a mutter (if you should
answer). The box checks that it is a cache for the IA: HA address mapping table for each connected LAN.
Situation 1: If this host mapping is found in the cache corresponding to the requesting LAN,
The box does not answer (let the host yourself should respond.). The entry is timeout no longer reset.
Case 2: If this host mapping is found in the cache corresponding to the non-issued LAN,
The box issued a response and gives him the HA address in the LAN in the request. Extra super
No longer reset.
In this case, the box is an agent of the target host. When an IP data reports
When this box, the box must try to forward it with the information in the address mapping cache.
Situation 3: If you can't find that map in any cache, the box must try to find this address, then respond like the case 1 or the case 2.
The box keeps a searcher (but not found) search table. Each table item contains a blog
The HA address and the source address of the original request host and the interface to which this ARP are received. Be in the case
3 Check this search list when you happen. If the host is already included in this search list
In the middle, it will end; otherwise, the table is spread.
In order to spread this search list, write a table entry on this search list, then organize
And send this ARP package on all interfaces. These ARPs requests HA, IA containing boxes
Address, the IA address of the host, and a request to the host HA address. If you receive
This ARP response, this information is entered into the corresponding cache, and the corresponding table item is in the search list.
Delete, then like the situation 1 or the case 2 to give the "ARP" host
An answer. If you don't receive a response, stop and don't make anything - no answer
Send that "trigger" host (entry still stays in the search list).
Note: The box must use its ARP request to try the number of attempts, if ordinary
Host ARP requests usually do 5 times, then it should also be 5
Attempt time.
In order to stop search, stop and do not make anything - no answer to the "trigger"
Host (entry is still left in the search list). There is no negative of the request to the ARP request
Feedback information, so it is impossible to judge the success of the search in addition to the timeout means.
For each ARP request received, the box must also put the IA: HA address of the sender.
Enter the cache corresponding to its local area network.
The entry in the cache and search list may time out.
In order to maintain a list of search lists, the termination must be followed: avoiding no responding host
Earnly successive ARP request. Once the host is included in the search list, the ARP request is not repeated. Such as
Fruits are turned on (or other non-response ARP request) host boot (or start responding to ARP
Ask), then, it is not available to the host on other networks before the entry timeout.
There are two ways to this question: the first is that the search list table item is timeout period. The second is to let the box
The child sends ARP for the search list.
There are several times in the program.
First, the host has tries to use ARP to perform address resolution. If the host is not responded, they can
It can be tried many times before getting it. We must also give the host in the length of time.
(It is called time T1) to establish a good evaluation method.
Second, there is a table item to stay in the list or from the box to generate an ARP address.
This time. Time T2.
Note: This time period T2 must be greater than the sum of T1 time in the largest loop of the LAN.
Again, the entry resisted in the cache of each local area network, called time t3.
The relationship between them must be satisfied: t! One suggestion is T1 less than 1 minute, T2 is less than 10 minutes, T3 is less than 1 hour. If the environment is very stable, the T3 becomes long can cause the number of search times to be less (ARP traffic Small sales). If the environment is not stable, the T3 becomes shorter to adapt faster. Another scheme is that the timer of the entries in the cache each time, and establishes a more Small T3 value. This will result in frequently used tables to stay in the cache, but few entries are used. It will be lost soon. Unfortunately, there is no necessity between frequent use and correctness. It will also cause a long period of time in the cache for a long time, if now The receipt of the address mapping ARP request is just less than the timeout cycle. Handling regular data reports, box Return the Survival Time (TTL) of the IP Packet and Update the header checksum of the IP packet. If TTL becomes 0, the packet will be discarded (not forwarded). ARP (according to current definition) is best obtained to get the most recent and outdated information. (exist Connecting to the complex multi-local area network environment A host on other local area networks Get two (or more) ARP requests. The first answer may come from the box, this is The most effective path. Here is a change in ARP host information to prevent more information from replacing the first back. answer. possible problems Illegal caching entry If the error information enters the cache entry, it will stay in some time (T3). The presence of old information Block communication (for a while), if the host changes its HA: IA address mapping. The method of replacing illegal or timeout entries in the cache is to make the box clearly agree with the broadcast ARP Released to request a table with the original HA: IA mapping with a new HA: IA mapping. item. An important server is also used to send (broadcast ARP answers) when they appear. Non-ARP host All ARP hosts or non-ARP hosts on the same LAN is not practical, so they have to send I hope they can communicate with each other. All hosts are non-ARP hosts in the next header Get an investigation. Hosts that cannot implement ARP must use other address mapping methods. They have to save one of all Host's full table, either access the above table in the server through a protocol, or count on the base The route judged by the analysis in the site domain. Non-broadcast local area network If the local area network connected to the box does not have broadcast capabilities or hosts on the local area network cannot respond ARP, then set up a quiet for that local area network (or address calculated from another address) State or dynamic HA: IA address table. The host on the domain online must be listed in the table. When the box can find the address map and send another ARP request to enter the non-broadcast local area network (only It is likely to happen when all hosts are included in the table and being filed in a non-broadcast local area online. When it is changed to send an ARP type request specifically to each box on the local area. Table size The worst table size in the box is a number of hosts in all local area networks. That is, for each local area network The table maintained by the interface may (in the worst case) Increase the establishment of each host on the entire LAN. However, these tables are actually satisfied The cache of the items required for the current communication activity, and this typical situation is far from being worst. Most hosts are mainly communicating with their local area hosts and host communication with other localities. Most of the communication on the LAN is the communication between the workstation host and the server host. We expect package High-frequency communication between the main server and other server hosts is placed in most boxes. Infinite transmission loop The likelihood of infinite transmission loop throughout the local area network interconnection can be through the search columns in the maintenance box Table and the search when a list is included in the list is included in the list. The transmission circuit of the periodic packet cannot be continued because the box must consume TTL, when the data packet is TTL will be discarded when 0. In order to debug, It is very useful to report to a box to report all the datagram discard. broadcast Note that broadcast does not do anything to transparent subnets or explicit subnets. I have already discussed in [1] It will be discussed again here. Two of the three broadcast functions pointed out in [1] Consistent and have the same result. The third also gives support. For the broadcast of IA address, the explicit subnet and transparent subnet are also a big debate. Points should be treated separately. It also implies that we do not need broadcasting technology. Instead, multi-playback technology has a good job. can. Learn how the Internet multi-playback works before accepting broadcast technology is wise. IP network If the IA network number is used and the host number is 1 (eg, 36.255.255.255), IP will broadcast all hosts of this network (ie, local local area network), which has been predetermined. Box will turn Send this dataset. The box will check this datagram to see if it has potential meaning. To prevent infinite transmission loops, the box must maintain a list of current broadcasts. All items in the table are from The source Ia and identification domain of the data header. If you receive a radio and a list of deleted items If you match, don't forward it. The timeout time of the entry is T2. Local area network All bits of IA are one (e.255.255.255.255) Book for all the Lords on this LAN The machine is broadcast broadcast. The box must not be forwarded. The box must check this datagram. Significance. Other LAN This method cannot be used because some local area networks are not indicated separately in IA. Some people have already discussed On this issue, it is considered to be a boring function. When providing a method of providing a special IA for each local area network that wants to broadcast. Such as, 36.255.255.128 means broadcasting on a LAN and 36.255.255.187 means in B Online broadcasting, etc. These addresses are connected to a special local area network with dedicated interpretation. Explanation. Other boxes should handle these addresses to other boxes. Explain these addresses The place is converted into broadcasts of this LAN. discuss This expansion ARP requires that the general host does not know that it is located in multiple local area network environments. If the host is analyzing its IA: HA address mapping, it may find a few To the IA mapping of the same HA. And if he takes timing measurements, it may be found that some host delays are more Other short. Further, it is possible to find the inner connection between these findings. But there are very few host opportunities I have encountered these troubles. Address structure In an explicit subnet scheme, some IA bits are dedicated to determining subnets (such as local area networks). Address Network, subnet and host domain. Typically, the distribution address density in the application of each domain is used. The decline, that is, the utilization rate of address space is reduced. The main implementation problem may appear, if installed The subnet is more planned and this must change the subnet. For use with Class C IA address Realistic subnet schemes seem to be completely impossible. For extended ARP schemes, the network and host domain in the address are simple. Extended ARP scheme available The IA address of any type. Host relocation technology In an explicit subnet program, when the host is pulled out from a local area and insert another LAN, its IA Must be changed. For extended ARP solutions, in this case, the original IA address is used. Through various circumstances, we see that there are two problems: 1. How to find the host if the target is on this LAN or other local area network? This situation assumes that the host understands the differences in these two situations and knows that in that case What to do? For further words, the host must not only know if he wants to answer him. Also know how to send data (eg, directly to the host, or box). Here, the host does not know the difference and always do the same thing. 2. How does the box of the LAN to know which one of the local area networks is to which one. 3. This situation assumes that the box needs some topology knowledge and interchanges the box to the box about connectivity. Agreement information. Here, the box does not know the topology knowledge and don't know how to know the green box. exist. Here, there are two problems that exist: First, the host is routing; second, how is the box? Sample routing. The requirements of the policy meeting uses a method for each issue, and one should be selected. Solution, part from one method part from another method. For example, using ARP inside the LAN, let the box send ARP response and act as a proxy (like the extension ARP scheme). But through the box to the box The agreement to use "which secretary is in" information to enter each box (Like the explicit subnet scheme). There are two places containing code: a large number of hosts and a small amount of box. Considering explicit subfamous The alternate use of the ARP scheme, the workload in the host is more important than the workload in the box. What does the host do? Explicit subnet solution The host must determine whether the IA is located on a local area or on other local area. if Located on this LAN, use some programs to find this IA; On the LAN, use some programs to find the IA address of the box. Extended ARP solution No matter which case uses ARP to get IA: HA mapping. What does the box do? Explicit subnet solution The box must determine which local area is located in the local area. It must be established Routing Table to tell each of the local area networks to send data from which interface News. This routing table must be kept until it is over, the box is to the box agreement on the Internet The gateway to the gateway protocol is very similar. Extended ARP solution The box must have a cache for each connected LAN's IA: HA mapping, but also Hold a search list. He doesn't have to run any box to the box agreement or even don't know Any other box existence. Topology and complexity of its implementation tree If the local area network and box constitute a tree structure, the box is very simple, do not have to keep search lists, Because there is no ARP request loop to move back and forth. Loop If there is a loop inside, then the search table is necessary. If the topology keeps quite stable, As for a long loop (all loops have the same size), and each local area network is in delay Keep compatible, the program described here will work very well. Complexity If the structure is very complicated, the structure is unstable, and / or there are many different types of bureaus that delay gap. The domain network mix is composed, then the box to the box protocol is a better choice. to sum up If Internet organizations can agree on multi-local area network issues and urge workstation manufacturers with the same middle sound It is very beneficial to establish a solution based on this. I strongly recommend it to extend the ARP scheme. I think most of the workstations will connect to a local area with broadcast capabilities. I think most of the workstations will For places where the explicit subnet scheme is not used, and will be used in the appropriate (explicit subnet unbearable) Class C IP The address of the address. So I think that the manufacturer supports ARP on the workstation to be the best way. I still think that I We should start working and create, develop, test and produce "Magic Box", and I am so strong because of them It is useful . Please note: Directs only a detailed routing program or box to the box protocol. this is Because such a routing program is very difficult. The suggestions provided here will make us start with reasonable parties Method application Multi-LAN Environment. If we have determined a routing program between the box, we only need Reforming the box without having to pay a host. Glossary ARP Address resolution protocol (see [1]). box Magic box. The box (computer) connects one or more local area networks of the same network. Can also be called "Based on ARP bridge ". bridge A node (computer), connecting two or more management, but physically separating Subnet, automatically forward the dataset if necessary, but he does not know its existence. "Called" soft relay " Datagram Communication units on the IP layer. Explicit subnet A subnet, IP address is explicitly labeled by one subnet address domain, and for this and foreign network It is also visible. Gateway A node (computer) is connected to two or more networks and / or subnets, forwarding The host is transmitted to it. HA Hardware addresses, this place is dedicated to the Packet of LAN. Host number The network internal host address, the low byte section of the IA. IA The Internet address is defined by the IP. Interconnect A collection of internet (such as a famous catnet). A group of networks that interconnect using IP. IP Internet protocol (see [3]). Lan local area network. Multi-LAN network It is considered a group of local area networks, such as, generally using a network number. Single LAN With a significant subnet or can be a transparent subnet. The internet Single Internet (which is likely to be divided into subnets or multiple local area networks), with a single network number to refer to Indicated. Network number A high byte section of an IP network number and IA. package Communication unit of the local area hardware layer. Subnet A subnet of a network. Part of the network (logical or physical). Transparent subnet Subnets that do not use the Internet address, so they are invisible to other networks (see Multi-LAN . TTL The living time domain of IP. references: [1] J. Mogul, "Internet Subnets", RFC-917, Stanford University, October 1984. [2] D. Plummer, "An Ethernet Address Resolution Protocol OR Converting Network Protocol Addresses to 48-Bit Ethernet Addresses for Transmission On Ethernet Hardware ", RFC-826, Symbolics, November 1982. [3] J. Postel, "Internet Protocol", RFC-791, USC-ISI, September 1981. RFC925 - MULTI-LAN Address Resolution Multi-LAN address resolution 1 RFC Document Chinese Translation Program
