| 315 | | As indicated in the comments, the top portion of the configuration listens ('''!FromDevice''') for IP packets arriving on the interface connected to '''hostA''' (that's '''eth3''' in this example). It then creates a new 16-byte field at the head of the packet (two bytes added by the '''Unstrip''' operation, plus the existing 14-byte Ethernet header. It fills that field with what could be important routing instructions, but in this case is just graffiti ('''!StoreData'''). The '''route''' operation then routes the packet via either the '''left''' or '''right''' router toward '''hostB'''. In either case, it wraps the packet in a fresh Ethernet header ('''!EtherEncap''') with a distinctive ether type code (0x7744), logs the new packet on its way out ('''Print''') and sends it out on the correct interface ('''!ToDevice'''). |
| 316 | | |
| 317 | | The bottom portion of the configuration is intended for packets coming out of the core network to '''hostA'''. It accepts packets from either the '''left''' or '''right''' router, logs them, strips off thirty bytes (Ethernet header plus your 16-byte new header field), puts on a fresh Ethernet header, and sends them along to '''hostA'''. |
| 318 | | |
| 319 | | The configuration for the '''bottom''' router is exactly symmetric, routing packets between '''hostB''' and the core network, but using different graffiti. |
| | 315 | |
| | 316 | Look in the [http://read.cs.ucla.edu/click/elements Click documentation] for more information about the elements in the above script. |
| | 317 | |
| | 318 | As indicated in the comments, the top portion of the configuration listens ('''!FromDevice''') for IP packets arriving on the interface connected to '''hostA''' (that's '''eth3''' in this example). It then creates a new 16-byte field at the head of the packet (two bytes added by the '''Unstrip''' operation, plus the existing 14-byte Ethernet header. It fills that field with what could be important routing instructions, but in this case is just graffiti ('''!StoreData'''). The '''route''' operation then routes the packet via either the '''left''' or '''right''' router toward '''hostB'''. In either case, it wraps the packet in a fresh Ethernet header ('''!EtherEncap''') with a distinctive ether type code (0x7744), logs the new packet on its way out ('''Print''') and sends it out on the correct interface ('''!ToDevice'''). |
| | 319 | |
| | 320 | The bottom portion of the configuration is intended for packets coming out of the core network to '''hostA'''. It accepts packets from either the '''left''' or '''right''' router, logs them, strips off thirty bytes (Ethernet header plus your 16-byte new header field), puts on a fresh Ethernet header, and sends them along to '''hostA'''. |
| | 321 | The configuration for the '''bottom''' router is exactly symmetric, routing packets between '''hostB''' and the core network, but using different graffiti. |
