SmartARP: Making Gigabit Networks Cheap

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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: 10.0.0.10

MAC: 00:00:aa:aa:aa:aa 

IP: 10.0.0.13

MAC: 00:00:dd:dd:dd:dd 

IP: 10.0.0.12

MAC: 00:00:cc:cc:cc:cc 

IP: 10.0.0.11

MAC: 00:00:bb:bb:bb:bb 

A 

D 

C 

B 

Dest

MAC 

Source

MAC 

Dest  IP 

Source  IP 

Data 

Ethernet frame 

IP packet

     

ARP: finding the MAC Address 

Host A 

Host B 

ARP Query 

ARP Response 

Broadcast 

Host B

MAC ? 

Host B

IP 

Host B

MAC 

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 

1 

2 

3 

4 

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 10.1.0.0/16 

Workgroups are

assigned smaller continuous ranges of IP addresses  

10.1.1.0 -

10.1.1.255 

10.1.4.0 -

10.1.4.255 

10.1.3.0 -

10.1.3.255 

10.1.2.0 -

10.1.2.255 

A 

C 

D 

B

     

SmartARP config file 

10.1.1.0  255.255.255.0  local

10.1.2.0  255.255.255.0  forward 00:01:3a:4c:12

10.1.3.0  255.255.255.0  forward 00:73:18:a5:62

10.1.4.0  255.255.255.0  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 00isco IOS like00interface for easy use      

Advanced SmartARP features 

10.1.1.0    255.255.255.0      LOCAL

10.1.2.0    255.255.255.0      FORWARD  00:00:00:11:11:11

10.1.7.2    255.255.255.255  CONST    00:00:22:d5:e6:f7

10.1.3.0    255.255.255.0      IP       00:11

10.1.3.1    255.255.255.255  SILENT

10.2.2.0    255.255.255.0      DNS      mac.mydomain.com

10.3.3.0    255.255.255.0      PROXY    10.1.1.2  

Action 

Parameter 

IP 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 

24 bits 

0000.3c12. 3456 

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 (TNNC009 Conference Proceedings) SmartARP software available at:  http://www.ltn.lv/~guntis/smarp/ Contact authors for latest smartARP versions:  guntis@taide.net, asid@lmt.lv, janis@latnet.lv, k.ogsts@konts.lv, jonis@mt.lv

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