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Network Working Group D. L. Mills
Request for Comments: 975 m / a-com linkAbit
February 1986
Autonomous federation
(Autonomous Confederations)
The state of this memo
The purpose of this RFC document is to make some improvements to the External Gateway Protocol (EGP), so that it supports a simple
The multi-layer routing capability does not impair the robustness of the current EGP model. This memo also needs to discuss and recommend
With further improvement, it has no restrictions.
Summary
This improvement effectively expands the concept of the core system to cover multiple autonomous system communities - called autonomous joints
State, existing implementation can work with enhanced implementation without modification. Autonomy compared to the general autonomous system
The fedection maintains a higher mutual letter, including reasonable protection of routing cycles between member systems, but allows relaxation
The routing limit of the current EGP model.
Improve the "hop number" or distance field including the EGP update message, the current EGP model does not incorporate this word
Interpretation of the paragraph. Each self-governing federation gives this field to support the routing of up to three layers: one is self
In the system, the second is in the homemade federal, and the third is in the federal whole, and the third layer is optional.
table of Contents
1 Introduction Background 2
1.1 External Gateway Agreement (The Exterior Gateway Protocol) 2
1.2 Route Restrictions 3
1.3 examples and problems (Examples and quest) 3
2 autonomous system and federal 4
2.1 Topology Model Topological Models 4
2.2 Credit Routing Specifications Trusted Routing Metrics 5
3 Problem in implementation (Implementation Issues) 5
3.1 Database Management Function (Data-Base Management Functions) 6
3.2 Route Function (Routing Functions) 6
3.3 Compatibility issues (Compatic Issues) 6
4 Summary and Conclusion 7
5 References (References) 7
1 Introduction and Background
The historical development of the Internet external gateway routing algorithm is derived from a fairly strict restricted topology model that emphasizes health.
Strong and stability, but the cost is the dynamics and flexibility of the route. Developing robust and flexible routing algorithms have been implemented
Practice has proved to be very difficult, and the reason is more due to the different understandings of services, rather than engineering issues.
The initial external gateway model is proposed in RFC 827, which is later redefined in RFC 888. This model strictly limits the Topology structure of the Internet as a tree structure, and the root is represented by the "core" gateway system developed by BBN. This
The most important feature of a model is to eliminate the routing cycle of resource, the gateway in the tree topology (called autonomous system)
There is impossible to have a routing cycle. However, even if the performance is not considered, there is still difficult, difficult, difficult, difficult, difficult
It is widely used.
1.1 External Gateway Agreement (The EXTERG GATEWAY Protocol)
To implement the close collaboration between the BBN core gateway and other organizations, the close collaboration between the gateway members, it is necessary to develop a middle
The protocol exchanges achievability information, but does not need to have a true routing algorithm. This agreement is called the external gateway association
Discuss (EGP) and is proposed by RFC 904.
The EGP is not designed as a routing algorithm, because it is unable to agree on a trustworthy, universal standard.
Instead, EGP is designed to provide high quality achievability information for approximate gateways and non-adjacent gateways. Current hair
Exhibition, dynamic routing is calculated and used by the core system and uses EGP - only as an interface mechanism - provided
Give the non-core gateway. Non-core gateways can provide routing for core systems or other non-core gateways, and single numbers cannot be passed
The "third party" route obtained by calculating data from other gateways.
With the accumulation of EGP practical experience, in order to avoid the waste of resources with no fully optimized, development
A more dispersed dynamic routing capacity is increasingly necessary. In addition, some people oppose the premise assumption of a single core system,
It is believed that this means that incomplete optimization performance, management problems, no practical mandation, and destruction that may bring
Sex. Regardless of whether these observations are definitive or fair, there is still an important technical issue: whether there is no display
Reduce stability and robust, and more dynamic, distributed methods?
This paper proposes an improvement to EGP, which promotes the concept of core systems, and incorporates multiple autonomous systems.
Universified community, and called a self-governing federation. Compared with the general autonomous system, the self-governing federation maintains a higher mutual letter.
It includes reasonable protection of a routing cycle between the member system. This enhancement includes "hop count" for EGP update messages
Or distance fields will be given a detailed explanation. It should be noted that RFC 904 does not make regulations for this field.
Just reserve it for later research.
Interpretation of the distance field consists of three levels of specifications. The lowest layer of which can be used for the internal network of the autonomous system itself
Off Agreement (IGP) and extends to internal routes within the scope of the autonomous system. A slightly high layer selection from the autonomous system to it
The preferred route of his autonomous system, and the third floor - is also the highest layer - select from the self-governing federation to other autonomy.
The preferred route of the federal.
It is convince that the model recommended here can be compatible with the current specifications and actual applications in the Internet. fact
On, now the autonomous system overall - including core systems - can be considered a self-governing federation, and if necessary
It is also possible to construct a new federal from an existing or new system.
1.2 Route Restrictions (Routing Restrictions)
The purpose of RFC 904 is to specify routing restrictions to replace the original files, including RFC 827 and RFC 888.
Non-core systems must not pass the views of third party information, and the RFC904 pre-account before the previous document is released.
Planning. This will effectively abolish the concept of "root" and other asymmetry, only
Use a third method.
In this way, there is only one restriction of the non-core system - only in its EGP message: (a) belongs to the same autonomy
The gateway of the system (internal neighbor); (b) the network that can be reached through the gateway belonging through the system. There is no other clear or implicit limit. This specification does not involve the design of the core system and its gateway.
This constraint means that in order to ensure complete connectivity, each non-core gateway must be transported with a core gateway.
Row EGP. Since the current core gateway implements other gateways on the EGP neighboring path, this is further implicit
Each non-core gateway must share a network with at least one core gateway.
Note that logically does not disable the EGP as IGP, and there is no limit to the use of other non-core systems.
EGP, if each gateway of each system runs EGP with each gateway of other systems, then the concept of the core system
It is unnecessary and extra.
During the development of the EGP model, the autonomous system must be a strict hierarchical topology (tree structure),
But now it is not needed. The two networks have been banned from connecting through the gateways of two or more systems, and now it is not required.
The autonomous system is a gateway instead of a network or a host, so a given network or host can pass different
The system arrives, but each gateway must only belong to a system.
1.3 examples and problems (Examples and Problems)
Consider an ordinary situation, two local area networks A and B are connected to the Arpanet through the gateways of different systems.
Now, the A and B are connected to the A-B gateway that belongs to the A-Arpanet belongs to the same system, so A-Arpanet
It can be included in the EGP information to other gateways, because both now are in A-Arpanet
The system is up to date. But the B-Arpanet Gateway can only be included in its own and B network, because A-gateway is not in its system
Initially.
In principle, we can assume that there is still a B-A gateway in the same system in the same system in the same system.
You can also be included in the A Net; however, two systems may be easier to treat the A-B gateway by negotiation. This negotiation
It may not be very straightforward, but because the combination gateway must be seen by other gateways as two completely different gateways, you must have
The respective autonomous system numbers.
Another situation is due to such a reason, a system does not have a path to the core gateway, but can only pass
Other non-core gateway connections. For example, there is a local area network C and one does not belong to A-Arpanet and B-Arapanet
Gateway C-a. According to the above limit, the gateway C-A can be sent to the EGP information to the A-Arpanet in the C network.
A-ARAPNET can also send itself to the EGP information to C-A, but other networks cannot be obtained from the core system.
these messages. In this way, the gateway C-A cannot achieve complete routing information unless it is directly running with a core gateway.
EGP.
2 autonomous system and federation
The second example described above illustrates a mechanism that allows two non-core gateways to exchange any routing information, while
Reduce - Correctly - coordinated security model - the level of robustness. One way is to extend existing single-core autonomy
The system model introduces a multi-core system. This requires a topological model to define the scope of these systems and a global trusted
Metrics are used to push routing. The next section describes a suitable topological model, and the appropriate metric is in the subsequent section.
.
2.1 Topology Model Topology Models
"Autonomous System" includes a collection of gateways, each can arrive at the same department only through the gateway inside the system
Any other gateway. The gateway within the system uses the internal gateway protocol to jointly maintain a routing database and one
Internal system trusted path mechanism (no longer discussed here). People hope that IGP includes security mechanisms to ensure the same department
The gateway inside the trick can be understood in the neighbors.
One or more gateways in the autonomous system can run the EGP with one or more gateways within the adjacent system. No
Limit the number and configuration of the EGP adjacent path, just require that the gateway included in each path must be within these two systems
Three systems that do not insert. In particular, the EGP neighbor must share the same network, although it is likely to be like this.
"Autonomous Federation" includes a collection of autonomous systems, and they share a public security model, that is, they
Trusting each other's routing of other systems within the federal computation of each other. Each gateway in the federality can be in the federal
The path arrived in other gateways in the same federation. Although there is no limit to the number of EGP paths in addition to the above constraints.
Set, it is still necessary for certain mechanisms to determine that the possible EGP neighbors are indeed in the same federation. For example, you can use access control.
The number of lists or number of division systems is achieved.
If a gateway within the system has an interface of a network, then from the autonomous system to this network is "direct
Can be reached. Each gateway within this system is eligible to include all direct access to the EGP information and send it to
Other systems. Generally, there may be a special network to be directly accessible from multiple systems.
From a self-government system to a network is "up to", if it is from a self-government system belonging to the same federation to this
A network is directly up to. A direct access to the same system is always accessible. Each gateway in the federation
They are eligible to include all accessible networks into EGP information and sent to any other system. A network may appear
Can directly reach from different federations.
In order to maintain the stability of the Internet global route, it is clearly assumed that from one autonomous system to a direct
The network is always prioritizing the path outside the system, and the path within the autonomous federation is always prioritizing the road of the federal exterior.
path. The next section discusses the mechanism to ensure this assumption.
In general, the EGP update information can include two gateway lists, one belonging to those gateways (internal)
Neighbors), one is a gateway (external neighbor) that belongs to different systems. Direct networks must have been with the same system
The gateway is connected to the internal neighbors, rather than direct access to the internal neighbors can also be connected to the external neighbor. can
But not directly to the network must be connected to the gateway in the same federation.
2.2 Trusted Routing Specifications Trusted Routing Metrics
It seems that there is a general rule that can portray the characteristics of the distributed system: the more touching things, the more energetic and more trustworthy.
Lai, the more far things, the more stubborn, the more doubtful. For example, the concept of network is inherent, put them inherent.
The gateway concept that is tied together is also inherent. A coper gateway close to each other (such as in a self-government)
Use high-performance routing algorithm to exchange routing information, can be keenly monitor, quickly adapt to performance indicators
Such as queue delays and connection load.
However, the gateway to each other is usually only a rough routing letter from the distance from each other.
Interest, it may be just the clues of the most likely next hop from the region. On the other hand, as the distance increases
This guess is also deepening, so these gateways may require fine safety considerations, including peer verification, confidentiality,
Confidential and signature confirmation. In addition, efficiency considerations often require a reasonable network bandwidth that the routing protocol itself will occupy.
The distance is increased and reduced. As a typical response to these two aspects, the farther distance between the gateways, the routing algorithm
The smaller the motor.
The above observations indicate that a global acceptable routing is required. Suppose this route specification is expressed as
An integer, the lower value represents a "closer" gateway that can accurately identify, the higher value representative can only be substantially identified.
"Far" gateway. If the value is less than a global recognized constant X, the autonomous destination is defined in the sender.
The route interior of the system is associated; if it is greater than this value but less than another constant y, the autonomous departure is
The route within the federal; if it is greater than y, it is associated with other routes.
In these three-layer-autonomous system, the homemade federal and federal all levels can run multiple ways at the same time.
By algorithm, each algorithm may generate different subtals and different specified values within the above predetermined range of each target network.
However, the interpretation of the specification value in each system must be the same, so other systems can mitigate the routes between multiple gateways within that system. Similarly, the interpretation of each federal value must also be consistent, so that other federal minus
The route between the gateways in the federal. Although all federals must meet a general federal overall algorithm,
However, the same federal algorithm is not used, and all systems in the same federation need to use the same system-level calculation.
law.
3 Implementation Issues
RFC 904 does not specify how 8 "hops" or distance fields in the EGP update message, but stay
After treatment. The above model provides the explanation of this field and implies how to design a corresponding routing algorithm.
In order to facilitate explanation, it is assumed that the values of the X and Y above are 128 and 192, respectively. This means that in the specific system "
The gateway will give the direct access to the distance value of less than 128, and the external gateway can freely compare these values and make
select. It also means that a gateway in a federal system will give those systems that are not directly accessible, but in the federal
The distance value between the thyed networks 128 to 192. In the discussion below, it is assumed that different federations can pass through 16-bit systems.
Certain features in the code field - maybe a retention subfield - identify,
3.1 Database Management Function (Data-Base Management Functions)
The following implementation model may help to further illustrate the above problems, and also provide at least one organizational gateway
According to the method of the library. The database is organized into a routing table, each record includes a network number and a list of items,
Each project is all from a) gateway address, the system number, the distance, b), B) Survival time counter, local
Routing information and other information required by the management database.
Whenever you receive an EGP update message from a neighbor, or other ways - such as system IGP, routing table
Will update. The message is first decoded, which makes up the group of the network number, gateway address, system number, and distance.
table. According to the EGP judgment, if the gateway address belongs to the inside of the neighboring system, the system number in the quad group is set to
The system number of the neighboring system; otherwise the system number is set to 0, indicating "external".
Then, according to the distance value provided in the message, the distance value of the heart is calculated according to the following conditions: if the system number and the local system
The number matching, the new distance value is determined according to the rules of the system IGP, but must be less than 128; otherwise, if the system number belongs to the same
A federation or system number is 0, and the original distance value is less than 192, then the new distance value is based on federal EGP rules.
Then determine, but should be greater than or equal to 128 and small 192; otherwise, this value is based on (global) federal overall EGP rules.
OK, but at least 192.
For each quad group in the list, the routing table looks for matching network numbers, and if not, a new record is added.
Then find the gateway address and system number matching that the network number in the project list. If you don't find a new
recording. Finally, recalculate the distance value, reset the living time field and add local routing information. All items in each list
The purpose of the purpose of life is increased according to the principle of regular. If a field exceeds a predetermined maximum, discard the project.
If all items in a list are discarded, the entire record includes the network number being deleted.
If the gateway sends an EGP update message to the neighbor, you must transpose data in order of the gateway address instead of the network number.
Library. This process needs to scan the routing table and select the shortest gateway to each network number. Result list follows the gateway
The address is sorted and divided according to the internal / external system number.
3.2 Routing Function (Routing functions)
The gateway encountered by the Data (Service Unit) retrieves the matching target network number in the routing table and selects the shortest gateway in that list. According to the above assignment method, it is clear that as long as there is a low level of the route, it will not select a higher level.
route. It is also clear that routing in the system does not affect the routing of the system, unless they are subject to the federal interior
Interference of routing algorithm. If the federal EGP uses simple minimum system hopping algorithms, each system IGP can only affect
The range of reaches.
3.3 Compatibility issues (Compaling Issues)
The interpretation of the distance field here is recommended, with the known EGP implementations that have not been explained in this field, and several already
Know privately use this field EGP implementation backward compatibility. The easiest way to develop existing systems is to
There are existing implementations that do not interpret the distance fields together as a federation, and use the existing core
Systems and routing limitations. All distance values provided by the federation are assumed to be 192, which is at least in the federal whole.
For basic path for roadworking ability.
One or more existing or proposed systems that use unanimous explanations of the distance field can be organized into one
Autonomous federation. This may contain those butterfly gateways or other compatible products that are now configured. These systems are available
The ability to select the route within the system in accordance with the distance field. It can be expected that if routing information comes from
Other butterfly systems then the distance field of the butterfly system must be set to be greater than or equal to 128; if the butterfly system is from
It is assumed that the distance from the federation is set to be greater than or equal to 192.
New system using the above recommended implementation model can choose to enter the federal route based on the distance field. But to be positive
Indeed, all systems and federals must consistently explain the distance values of more than 192.
4 Summation and Conclusion (Summary and Conclusions)
From the surface, this paper proposes a suggestion for explaining the distance field of the EGP update message. This field is originally
There is no structural explanation, but it is often informal. This proposal has always been to the system and federal structure
The autonomous system is sorted and the distance field is interpreted as a specifications of three levels. The result is formed three levels of levels.
The routing community, one is prioritizing the way in the system, one is preferred to find a way in the federal, and there is no set priority.
Part.
Although the proposed three-layer structure can be extended to any multi-layer, it will make the distance field very crowded - in the current
There are only 8 bits in the EGP model.
According to John Nagle and other people's suggestions, the concept of distance can be easily promoted as "management distance".
5 References (References)
[1] Rosen, E., Exterior Gateway Protocol (EGP), DARPA NETWORK
Working Group Report RFC-827, Bolt Beranek and Newman, September
1982.
[2] Seamonson, L.J., And E.c., Rosen. "Stub" exterior Gateway
Protocol, Darpa Network Working Group REPORT RFC-888, BBN
Communications, January 1984.
[3] Mills, D.L., Exterior Gateway Protocol Formal Specification,
Darpa Network Working Group Report RFC-904, M / A-COM LINKABIT,
April 1984.
RFC 975 - Autonomous ConfedeS
1
RFC Chinese Document Translation Plan
