SmartARP: Making Gigabit Networks Cheap Andris Sidorovs, Riga Technical University Janis Lacis, Latnet Karlis Ogsts, Tieto Konts Financial Systems Ltd. Guntis Barzdins, Taide Network AS Janis Dzerins, University of Latvia

Ethernet Most popular LAN technology nowadays 10Mb/s - 1Gb/s Each host has unique 48bit MAC address (factory assigned) Frames sent to MAC addresses Broadcasts widely used To find destination MAC address, ARP protocol is used IP: MAC: 00:00:aa:aa:aa:aa IP: MAC: 00:00:dd:dd:dd:dd IP: MAC: 00:00:cc:cc:cc:cc IP: MAC: 00:00:bb:bb:bb:bb A DC B Dest MAC Dest MAC Source MAC Source MAC Dest IP Source IP Data Ethernet frame IP packet

ARP: finding the MAC Address Host AHost B ARP Query ARP Response Broadcast Host B MAC ? Host B MAC ? Host B IP Host B IP Host B MAC Host B MAC Host B IP Host B IP Unicast RFC 826: Address Resolution Protocol, 1982

Interconnecting Ethernet LANs Departmental LANs in University Campus Requirements Interconnections must be fast Departmental Novell and MS Windows networks should be isolated Misconfiguration in one department should not disrupt network in another department Easy to configure ? ? ? ?

Interconnecting by Routers Departmental LANs in University Campus Advantages Contain broadcasts Filtering possible by protocol Disadvantages Slow (each packet intensively processed) Complex Expensive (especially for 100Mbps and 1Gbps)

Interconnecting by LAN Switches Departmental LANs in University Campus Advantages Fast (wire speed) Cheap Simple to install Disadvantages Do not scale, because broadcasts are not contained No filtering by protocol

Interconnecting by VLANs Advantages Single powerful router interconnects many VLANs Cisco Netflow and Routing Switches shortcut traffic Disadvantages Bottleneck is router Only expensive switches and routers support that Bottleneck VLAN 1 VLAN 4 VLAN 3 VLAN 2

Interconnecting by SmartARP Advantages Contains Broadcasts Effectively stops all protocols Fast (wire speed) Cheap (standard switches used) Disadvantages Nothing works unless smartARP used MAC Broadcast filter

SmartARP Server based ARP Transparent to hosts Uses queries instead of broadcasts Easy to configure (stateless) Only one needed per broadcast domain Available for free (runs on Win95 & Linux) Supports 10Mb/s, 100Mb/s, 1Gb/s,...

SmartARP operation MAC Broadcast filter SmartARP Server SmartARP Server SmartARP Server SmartARP Server X Y ARP Query ARP Reply Broadcast Unicast A B D C

SmartARP configuration MAC Broadcast filter SmartARP Server B SmartARP Server C SmartARP Server A SmartARP Server D Whole network is one big IP subnet /16 Workgroups are assigned smaller continuous ranges of IP addresses A C D B

SmartARP config file local forward 00:01:3a:4c: forward 00:73:18:a5: forward 00:0c:63:52:7a Configuration file of SmartARP server A: MAC address of smartARP server B MAC address of smartARP server C MAC address of smartARP server D Ranges of IP addresses assigned to workgroups

SmartARP implementation Win95

SmartARP implementation Linux Source code available Runs on multiple interfaces Can be used with Linux bridge Convenient pre-compiled version: –boots from single 1.44MB FDD (no HDD needed) –optionally acts as bridge with MAC broadcast filter –supports up to six NE2000 PCI compatible 10/100Mbps Ethernet cards –“Cisco IOS like” interface for easy use

Advanced SmartARP features LOCAL FORWARD 00:00:00:11:11: CONST 00:00:22:d5:e6:f IP 00: SILENT DNS mac.mydomain.com PROXY ActionParameterIP Address and Mask Like in routing, IP network number with longest prefix is preferred when selecting a SmartARP rule to be applied

How to filter broadcasts in switches? None of configurable Cisco, Bay, 3Com switches has such option (!!!) Use Linux bridge code - modify one line in source code to filter Broadcasts Use any Cisco router as Ethernet bridge: no ip routing bridge 1 protocol ieee bridge 1 address ffff.ffff.ffff discard interface Ethernet0 no ip address bridge-group 1 interface Ethernet1 no ip address bridge-group 1

Cheap Scaleable Ethernet: HANE Hierarchically Addressed Non-broadcast Ethernet –Ethernet without MAC broadcasts –48bit MAC addresses are not factory assigned, but are configurable like IP addresses (32bit IP address can be part of 48bit MAC address) –Ethernet switches use prefix based MAC switching tables HANE is the way to go: it is cheap, fast, scales to global networks, and is compatible with existing networks.

How to change MAC address? 24 bits c Vendor Code Serial Number ROM RAM Factory assigned unique MAC address is burned into ROM, but the MAC address actually used by the card is stored in RAM MAC address is configurable in Win95, NT, UNIX, Cisco routers (instructions provided in Full Paper) Interface driver copies MAC address from ROM into RAM by default, if no explicit MAC address is supplied to the driver

Final More details appear in Full Paper (TNNC’99 Conference Proceedings) SmartARP software available at: Contact authors for latest smartARP versions: