FrameRelay-簡介及基本配置

Frame Relay現在越來越不流行了，不過在過去的設計中被廣泛應用。

所以工作上還是能經常見到的, 這篇博文從二層簡單總結下FR的一些概念

在介紹Frame Relay之前，先瞭解下廣播介質和非廣播介質的區別：

Broadcast Media （廣播介質）： Ethernet 、 Token-Ring、FDDI

特點：

源可以同時向所有串連（二層）目的地址通話簡化了三層到二層的解析

Non-Broadcast Multi Access （NBMA）： Frame Relay、ISDN、ATM etc。

特點：

源不能同時和二層相連的所有目的地址通話三層的廣播通過二層重複的單播實現 （pseudo-broadcast）

========三層到二層的位址解析對比=======

廣播介質的三層位址解析：遠程二層MAC地址和遠程三層地址綁定

- IPv4 Adress Resolution Protocol ( ARP)

廣播請求 - 誰知道1.1.1.1的MAC地址單播回複 - 我的MAC是abcd.abcd.abcd

廣播介質的三層位址解析：遠程或本地的二層MAC地址和遠程三層地址綁定

本地FR DLCI和遠程IPv4地址綁定遠端ISDN電話和原電IPX地址綁定

- 反向ARP用解析遠程三層地址到本地二層地址

- 只有直接相連的裝置可以進行解析

NBMA 連接埠類型：

多點介面 - 可串連多個二層鏈路 & 需要三層到二層的解析 (FR & ATM main interface)

單點介面 - 串連一個二層鏈路 & 不需要三層到二層解析 （PPP link, FR p2p subinterface)

======================================

1. FR 簡介

應用了NBMA - 也就意味著潛在存在三層到二層解析問題

DLCI - Data link Connection Identifier (數字鏈路識別碼）

二層定址DLCI本地有效

LMI - Local Management Interface

DTE or DCE 通訊彙報虛擬連結的狀態
2. FR LMI 配置 開啟FR - encapsulation frame-relay LMI的類型 ( 自動偵測） - frame-relay lmi-type 【cisco | ansi | q933a】 - show frame-relay lmi 驗證虛擬連結VC狀態 - show frame-relay pvc 狀態種類： - active （E2E是好的，至少router 到 switch是ok的） - inactive （中途出了問題） - deleted （ 路由器試圖用一些參數但是FR交換器不支援，配置錯誤等） - static （LMI is disabled，用於back to back FR)
3. FR 位址解析 - 多點連接埠需要三層到二層解析： 想要發包到IP a.b.c.d需要哪個DLCI ？ - 解析的種類 動態解析通過反向ARP請求 （inverse ARP）靜態解析通過命令frame-relay map - 驗證： sh frame-relay map
======= FR inverse ARP - 當配置了FR支援的協議，反向ARP自動開啟 - 請求會在連接埠配置的所有鏈路上發出 反向APR請求發送可以disable - no frame-relay inverse arp [protocol] [dlci]回複不能被disable （這是個潛在的問題） - 自動包括了對廣播的支援
FR static Mapping - 手動把本地的二層地址和遠端三層地址綁定 frame-relay map [protocol] [address] dlci [broadcast]和靜態ARP的邏輯一樣 - 靜態配置會覆蓋動態配置 - 想支援廣播的話需要手動設定 ========
路由器的Auto-install和Frame Relay可能引入問題： - 如果在NVRAM裡沒有設定檔，路由器會偵測連接埠的封裝模式和發送地址請求 LAN - DHCP HDLC - SLARP FR - BOOTP - 當地址配置過後，路由器就會試圖通過TFTP拿到配置
FR在這裡出現的問題在第四步： 偵測封裝通過DLCI學習LMI給所有DLCIs發送BOOTP如果請求失敗了，會自動設定0.0.0.0 mapping這可能破壞之後的路由配置解決方案就是save config and reload ================= 最後要提的是點到點連接埠
- 一個連接埠對一條二層鏈路 - 不需要三層到二層的解析，只需要配置鏈路號 - frame-relay interface-dlci [dlci] - 更傾向於點到點配置（可以避免三層以上配置問題）

================ 思科官方文檔 - 基本配置

An interface is by default a "multipoint" interface so, frame-relay inverse-arp is on (for point-to-point, there is no Inverse ARP). IP split horizon checking is disabled by default for Frame Relay encapsulation, so routing updates come in and out the same interface. The routers learn the data-link connection identifiers (DLCIs) they need to use from the Frame Relay switch via LMI updates. The routers then Inverse ARP for the remote IP address and create a mapping of local DLCIs and their associated remote IP addresses. 

Spicey

Spicey#show running-configBuilding configuration...Current configuration : 1705 bytes!version 12.1service timestamps debug datetime msecservice timestamps log datetime msecno service password-encryption!hostname Spicey!!!interface Ethernet0 ip address 124.124.124.1 255.255.255.0!interface Serial0 ip address 3.1.3.1 255.255.255.0 encapsulation frame-relay frame-relay interface-dlci 140!!router rip network 3.0.0.0 network 124.0.0.0!line con 0 exec-timeout 0 0 transport input noneline aux 0line vty 0 4 login!end

Prasit

Prasit#show running-configBuilding configuration...Current configuration : 1499 bytes!version 12.1service timestamps debug datetime msecservice timestamps log datetime msecno service password-encryption!hostname Prasit!!!interface Ethernet0 ip address 123.123.123.1 255.255.255.0!!interface Serial1 ip address 3.1.3.2 255.255.255.0 encapsulation frame-relay frame-relay interface-dlci 150!!router rip network 3.0.0.0 network 123.0.0.0!!!line con 0 exec-timeout 0 0 transport input noneline aux 0line vty 0 4 login!end

驗證

show frame-relay map

show frame-relay pvc

show frame-relay lmi

ping <device name>

show ip route

Spicey#show frame-relay mapSerial0 (up): ip 3.1.3.2 dlci 140(0x8C,0x20C0), dynamic,              broadcast,, status defined, activeSpicey#show frame-relay pvcPVC Statistics for interface Serial0 (Frame Relay DTE)              Active     Inactive      Deleted       Static  Local          1            0            0            0  Switched       0            0            0            0  Unused         0            0            0            0DLCI = 140, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0  input pkts 83            output pkts 87           in bytes 8144        out bytes 8408           dropped pkts 0           in FECN pkts0           in BECN pkts 0           out FECN pkts 0          out BECN pkts0           in DE pkts 0             out DE pkts 0           out bcast pkts 41         out bcast bytes 3652        pvc create time 01:31:50, last time pvc status changed 01:28:28Spicey#show frame-relay lmiLMI Statistics for interface Serial0 (Frame Relay DTE) LMI TYPE = CISCO  Invalid Unnumbered info 0             Invalid Prot Disc 0  Invalid dummy Call Ref 0              Invalid Msg Type 0  Invalid Status Message 0              Invalid Lock Shift 0  Invalid Information ID 0              Invalid Report IE Len 0  Invalid Report Request 0              Invalid Keep IE Len 0  Num Status Enq. Sent 550              Num Status msgs Rcvd 552  Num Update Status Rcvd 0              Num Status Timeouts 0Spicey#ping 123.123.123.1Type escape sequence to abort.Sending 5, 100-byte ICMP Echos to 123.123.123.1, timeout is 2 seconds:!!!!!Success rate is 100 percent (5/5), round-trip min/avg/max = 36/36/40 msSpicey#show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-ISinter area       * - candidate default, U - per-user static route, o - ODR       P - periodic downloaded static route Gateway of last resort is not set     3.0.0.0/24 is subnetted, 1 subnetsC       3.1.3.0 is directly connected, Serial0     124.0.0.0/24 is subnetted, 1 subnetsC       124.124.124.0 is directly connected, Ethernet0R    123.0.0.0/8 [120/1] via 3.1.3.2, 00:00:08, Serial0

Prasit#show frame-relay mapSerial1 (up): ip 3.1.3.1 dlci 150(0x96,0x2460), dynamic,              broadcast,, status defined, activePrasit#show frame-relay pvcPVC Statistics for interface Serial1 (Frame Relay DTE)              Active     Inactive      Deleted       Static  Local          1            0            0            0  Switched       0            0            0            0  Unused         0            0            0            0DLCI = 150, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial1  input pkts 87            output pkts 83           in bytes 8408        out bytes 8144           dropped pkts 0           in FECN pkts 0           in BECN pkts 0           out FECN pkts 0          out BECN pkts 0           in DE pkts 0             out DE pkts 0           out bcast pkts 38         out bcast bytes 3464        pvc create time 01:34:29, last time pvc status changed 01:28:05Prasit#show frame-relay lmiLMI Statistics for interface Serial1 (Frame Relay DTE) LMI TYPE = CISCO  Invalid Unnumbered info 0             Invalid Prot Disc 0  Invalid dummy Call Ref 0              Invalid Msg Type 0  Invalid Status Message 0              Invalid Lock Shift 0  Invalid Information ID 0              Invalid Report IE Len 0  Invalid Report Request 0              Invalid Keep IE Len 0  Num Status Enq. Sent 569              Num Status msgs Rcvd 570  Num Update Status Rcvd 0              Num Status Timeouts 0Prasit#ping 124.124.124.1Type escape sequence to abort.Sending 5, 100-byte ICMP Echos to 124.124.124.1, timeout is 2 seconds:!!!!!Success rate is 100 percent (5/5), round-trip min/avg/max = 36/36/36 msPrasit#show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-ISinter area       * - candidate default, U - per-user static route, o - ODR       P - periodic downloaded static routeGateway of last resort is not set     3.0.0.0/24 is subnetted, 1 subnetsC       3.1.3.0 is directly connected, Serial1R    124.0.0.0/8 [120/1] via 3.1.3.1, 00:00:19, Serial1     123.0.0.0/24 is subnetted, 1 subnetsC       123.123.123.0 is directly connected, Ethernet0

參考資料：

Comprehensive Guide to Configuring and Troubleshooting Frame Relay