1 .OS specs:
fc4 2.6.15.4
network adaptor: realteck 8139 (built-in on Intel 855me)

2. command output discr'p:
"ifconfig -a" outputs CORRECT ip address and configuration
"ping .." succeeded.
"cat /etc/resolv.conf" gives right contents (as shown when using original kernel 2.6.11)

3. errors on screen (when booting):
-----
staring service network" rtnetlink answers:invalid argument
bring up eth0 interface: rtnetlink answers: invalid argument
determing ip... :network unreachable
rtnetlink answers: invalid argument
---------

4. my attempts (which will seduce me into endless trials of compiling)
(with the correct network device realtek 8139 selected and tcp/ip compiled)
eable all network device support and pcmcia device support and network options support, but FAILED

----
any help? (or further help this time)

well, solved just now, which as well gives solution to the problem:
"RTNETLINK answers:invalid argument"
that haunted kernel-compilers like me for days!
---
the key problem lies in: netfilter and ipv6
---------
1. disable "ipv6(exprimental)" from "netfilter"
2. disable UNNECESSARY or items recommended as "N (if unsure, choose N)
3. choose "ip router" and "ip multicast", "multiple tables"
----
here's mine on Networking Settings:
(section of a trimmed, working config)
-------
# Networking options
#
CONFIG_PACKET=y
CONFIG_PACKET_MMAP=y
CONFIG_UNIX=y
CONFIG_XFRM=y
CONFIG_XFRM_USER=y
CONFIG_NET_KEY=m
CONFIG_INET=y
CONFIG_IP_MULTICAST=y
CONFIG_IP_ADVANCED_ROUTER=y
CONFIG_ASK_IP_FIB_HASH=y
# CONFIG_IP_FIB_TRIE is not set
CONFIG_IP_FIB_HASH=y
CONFIG_IP_MULTIPLE_TABLES=y
CONFIG_IP_ROUTE_FWMARK=y
CONFIG_IP_ROUTE_MULTIPATH=y
# CONFIG_IP_ROUTE_MULTIPATH_CACHED is not set
CONFIG_IP_ROUTE_VERBOSE=y
# CONFIG_IP_PNP is not set
CONFIG_NET_IPIP=m
CONFIG_NET_IPGRE=m
CONFIG_NET_IPGRE_BROADCAST=y
CONFIG_IP_MROUTE=y
CONFIG_IP_PIMSM_V1=y
CONFIG_IP_PIMSM_V2=y
# CONFIG_ARPD is not set
CONFIG_SYN_COOKIES=y
CONFIG_INET_AH=m
CONFIG_INET_ESP=m
CONFIG_INET_IPCOMP=m
CONFIG_INET_TUNNEL=m
CONFIG_INET_DIAG=y
CONFIG_INET_TCP_DIAG=y
# CONFIG_TCP_CONG_ADVANCED is not set
CONFIG_TCP_CONG_BIC=y

#
# IP: Virtual Server Configuration
#
# CONFIG_IP_VS is not set
CONFIG_IPV6=m
CONFIG_IPV6_PRIVACY=y
CONFIG_INET6_AH=m
CONFIG_INET6_ESP=m
CONFIG_INET6_IPCOMP=m
CONFIG_INET6_TUNNEL=m
CONFIG_IPV6_TUNNEL=m
CONFIG_NETFILTER=y
# CONFIG_NETFILTER_DEBUG is not set

#
# Core Netfilter Configuration
#
CONFIG_NETFILTER_NETLINK=m
CONFIG_NETFILTER_NETLINK_QUEUE=m
CONFIG_NETFILTER_NETLINK_LOG=m

#
# IP: Netfilter Configuration
#
CONFIG_IP_NF_CONNTRACK=m
CONFIG_IP_NF_CT_ACCT=y
CONFIG_IP_NF_CONNTRACK_MARK=y
# CONFIG_IP_NF_CONNTRACK_EVENTS is not set
# CONFIG_IP_NF_CONNTRACK_NETLINK is not set
# CONFIG_IP_NF_CT_PROTO_SCTP is not set
CONFIG_IP_NF_FTP=m
CONFIG_IP_NF_IRC=m
# CONFIG_IP_NF_NETBIOS_NS is not set
CONFIG_IP_NF_TFTP=m
# CONFIG_IP_NF_AMANDA is not set
# CONFIG_IP_NF_PPTP is not set
# CONFIG_IP_NF_QUEUE is not set
CONFIG_IP_NF_IPTABLES=m
CONFIG_IP_NF_MATCH_LIMIT=m
CONFIG_IP_NF_MATCH_IPRANGE=m
CONFIG_IP_NF_MATCH_MAC=m
CONFIG_IP_NF_MATCH_PKTTYPE=m
# CONFIG_IP_NF_MATCH_MARK is not set
# CONFIG_IP_NF_MATCH_MULTIPORT is not set
# CONFIG_IP_NF_MATCH_TOS is not set
# CONFIG_IP_NF_MATCH_RECENT is not set
# CONFIG_IP_NF_MATCH_ECN is not set
# CONFIG_IP_NF_MATCH_DSCP is not set
# CONFIG_IP_NF_MATCH_AH_ESP is not set
# CONFIG_IP_NF_MATCH_LENGTH is not set
# CONFIG_IP_NF_MATCH_TTL is not set
# CONFIG_IP_NF_MATCH_TCPMSS is not set
# CONFIG_IP_NF_MATCH_HELPER is not set
# CONFIG_IP_NF_MATCH_STATE is not set
# CONFIG_IP_NF_MATCH_CONNTRACK is not set
# CONFIG_IP_NF_MATCH_OWNER is not set
# CONFIG_IP_NF_MATCH_ADDRTYPE is not set
# CONFIG_IP_NF_MATCH_REALM is not set
# CONFIG_IP_NF_MATCH_SCTP is not set
# CONFIG_IP_NF_MATCH_DCCP is not set
# CONFIG_IP_NF_MATCH_COMMENT is not set
# CONFIG_IP_NF_MATCH_CONNMARK is not set
# CONFIG_IP_NF_MATCH_CONNBYTES is not set
# CONFIG_IP_NF_MATCH_HASHLIMIT is not set
# CONFIG_IP_NF_MATCH_STRING is not set
# CONFIG_IP_NF_FILTER is not set
# CONFIG_IP_NF_TARGET_LOG is not set
# CONFIG_IP_NF_TARGET_ULOG is not set
# CONFIG_IP_NF_TARGET_TCPMSS is not set
# CONFIG_IP_NF_TARGET_NFQUEUE is not set
CONFIG_IP_NF_NAT=m
CONFIG_IP_NF_NAT_NEEDED=y
CONFIG_IP_NF_TARGET_MASQUERADE=m
CONFIG_IP_NF_TARGET_REDIRECT=m
CONFIG_IP_NF_TARGET_NETMAP=m
CONFIG_IP_NF_TARGET_SAME=m
# CONFIG_IP_NF_NAT_SNMP_BASIC is not set
CONFIG_IP_NF_NAT_IRC=m
CONFIG_IP_NF_NAT_FTP=m
CONFIG_IP_NF_NAT_TFTP=m
# CONFIG_IP_NF_MANGLE is not set
CONFIG_IP_NF_RAW=m
CONFIG_IP_NF_TARGET_NOTRACK=m
CONFIG_IP_NF_ARPTABLES=m
CONFIG_IP_NF_ARPFILTER=m
CONFIG_IP_NF_ARP_MANGLE=m

#
# IPv6: Netfilter Configuration (EXPERIMENTAL)
#
# CONFIG_IP6_NF_QUEUE is not set
# CONFIG_IP6_NF_IPTABLES is not set

#
# DCCP Configuration (EXPERIMENTAL)
#
# CONFIG_IP_DCCP is not set

#
# SCTP Configuration (EXPERIMENTAL)
#
# CONFIG_IP_SCTP is not set
# CONFIG_SCTP_HMAC_NONE is not set
# CONFIG_SCTP_HMAC_SHA1 is not set
# CONFIG_SCTP_HMAC_MD5 is not set
CONFIG_ATM=m
CONFIG_ATM_CLIP=m
# CONFIG_ATM_CLIP_NO_ICMP is not set
CONFIG_ATM_LANE=m
# CONFIG_ATM_MPOA is not set
# CONFIG_ATM_BR2684 is not set
# CONFIG_BRIDGE is not set
# CONFIG_VLAN_8021Q is not set
# CONFIG_DECNET is not set
CONFIG_LLC=m
# CONFIG_LLC2 is not set
CONFIG_IPX=m
# CONFIG_IPX_INTERN is not set
# CONFIG_ATALK is not set
# CONFIG_X25 is not set
# CONFIG_LAPB is not set
# CONFIG_NET_DIVERT is not set
# CONFIG_ECONET is not set
CONFIG_WAN_ROUTER=m

#
# QoS and/or fair queueing
#
CONFIG_NET_SCHED=y
CONFIG_NET_SCH_CLK_JIFFIES=y
# CONFIG_NET_SCH_CLK_GETTIMEOFDAY is not set
# CONFIG_NET_SCH_CLK_CPU is not set

#
# Queueing/Scheduling
#
CONFIG_NET_SCH_CBQ=m
CONFIG_NET_SCH_HTB=m
CONFIG_NET_SCH_HFSC=m
CONFIG_NET_SCH_ATM=m
CONFIG_NET_SCH_PRIO=m
CONFIG_NET_SCH_RED=m
CONFIG_NET_SCH_SFQ=m
CONFIG_NET_SCH_TEQL=m
CONFIG_NET_SCH_TBF=m
CONFIG_NET_SCH_GRED=m
CONFIG_NET_SCH_DSMARK=m
CONFIG_NET_SCH_NETEM=m
CONFIG_NET_SCH_INGRESS=m

#
# Classification
#
CONFIG_NET_CLS=y
CONFIG_NET_CLS_BASIC=m
CONFIG_NET_CLS_TCINDEX=m
CONFIG_NET_CLS_ROUTE4=m
CONFIG_NET_CLS_ROUTE=y
CONFIG_NET_CLS_FW=m
CONFIG_NET_CLS_U32=m
CONFIG_CLS_U32_PERF=y
CONFIG_CLS_U32_MARK=y
CONFIG_NET_CLS_RSVP=m
CONFIG_NET_CLS_RSVP6=m
CONFIG_NET_EMATCH=y
CONFIG_NET_EMATCH_STACK=32
CONFIG_NET_EMATCH_CMP=m
CONFIG_NET_EMATCH_NBYTE=m
CONFIG_NET_EMATCH_U32=m
CONFIG_NET_EMATCH_META=m
# CONFIG_NET_EMATCH_TEXT is not set
# CONFIG_NET_CLS_ACT is not set
CONFIG_NET_CLS_POLICE=y
CONFIG_NET_CLS_IND=y
CONFIG_NET_ESTIMATOR=y

#
# Network testing
#
# CONFIG_NET_PKTGEN is not set
# CONFIG_HAMRADIO is not set
CONFIG_IRDA=m
------
end of post!