Messages in this thread | ![/](/images/icornerl.gif) | | From | "Hen, Shmulik" <> | Subject | change_mtu boundary checking error | Date | Tue, 17 Apr 2001 05:29:05 -0700 |
| |
Hello,
Going through the change_mtu() code in the kernel, I came across the default function supplied when calling ether_setup(). I could see that eth_change_mtu() (drivers/net/net_init.c) does the following:
if( (new_mtu < 68) || (new_mtu > 1500) ) return -EINVAL;
Looking in include/linux/if_ether.h I found the following constants: #define ETH_ALEN 6 /* Octets in one ethernet addr */ #define ETH_HLAN 14 /* Total octets in header. */ #define ETH_ZLEN 60 /* Min. octets in frame sans FCS */ #define ETH_DATA_LEN 1500 /* Max. octets in payload */ #define ETH_FRAME_LEN 1514 /* Max. octets in frame sans FCS */
Now, the high boundary seemed reasonable (ETH_FRAME_LEN - ETH_HLEN = ETH_DATA_LEN) which gives 1500, but why is the low boundary set to 68 ? According to my calculations, it should have been ETH_ZLEN - ETH_HLEN which gives 46.
Doesn't mtu means only the payload size ? Where did the 68 come from ?
Thanks, Shmulik Hen Software Engineer Linux Advanced Networking Services Network Communications Group, Israel (NCGj)
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| ![\](/images/icornerr.gif) |